ci: update Travis-CI configuration

 * Add clang-6.0 to the build matrix (allowed to fail)
 * Upgrade xcode9 to xcode9.2
 * Various simplifications

Change-Id: I626006f79bbb7a1a79ec804c66ef30fef1e7cfd2
diff --git a/.jenkins.d/10-build.sh b/.jenkins.d/10-build.sh
index 255c7dd..d6f9e37 100755
--- a/.jenkins.d/10-build.sh
+++ b/.jenkins.d/10-build.sh
@@ -10,6 +10,12 @@
 git submodule sync
 git submodule update
 
+if [[ $JOB_NAME == *"code-coverage" ]]; then
+    COVERAGE="--with-coverage"
+elif [[ -z $DISABLE_ASAN ]]; then
+    ASAN="--with-sanitizer=address"
+fi
+
 # Cleanup
 sudo env "PATH=$PATH" ./waf --color=yes distclean
 
@@ -30,12 +36,7 @@
 fi
 
 # Configure/build in debug mode with tests and without precompiled headers
-if [[ $JOB_NAME == *"code-coverage" ]]; then
-    COVERAGE="--with-coverage"
-elif [[ -n $BUILD_WITH_ASAN || -z $TRAVIS ]]; then
-    ASAN="--with-sanitizer=address"
-fi
-./waf --color=yes configure --debug --with-tests --without-pch $COVERAGE $ASAN
+./waf --color=yes configure --debug --with-tests --without-pch $ASAN $COVERAGE
 ./waf --color=yes build -j${WAF_JOBS:-1}
 
 # (tests will be run against debug version)
diff --git a/.travis.yml b/.travis.yml
index 61c1139..5e45e4e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,6 @@
+language: cpp
+dist: trusty
 sudo: required
-language: generic
 env:
   global:
     - JOB_NAME=limited-build
@@ -8,150 +9,104 @@
 matrix:
   include:
     # Linux/gcc
+    # https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test/+packages
     - os: linux
-      dist: trusty
-      env:
-        - CXX=g++-4.8
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
+      env: COMPILER=g++-4.8
     - os: linux
-      dist: trusty
+      env: COMPILER=g++-4.9
       addons:
         apt:
           sources: ubuntu-toolchain-r-test
           packages: g++-4.9
-      env:
-        - CXX=g++-4.9
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=g++-5
       addons:
         apt:
           sources: ubuntu-toolchain-r-test
           packages: g++-5
-      env:
-        - CXX=g++-5
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=g++-6
       addons:
         apt:
           sources: ubuntu-toolchain-r-test
           packages: g++-6
-      env:
-        - CXX=g++-6
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=g++-7
       addons:
         apt:
           sources: ubuntu-toolchain-r-test
           packages: g++-7
-      env:
-        - CXX=g++-7
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
 
     # Linux/clang
+    # https://apt.llvm.org/
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-3.5
       addons:
         apt:
           packages: clang-3.5
-      env:
-        - CXX=clang++-3.5
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-3.6
       addons:
         apt:
           packages: clang-3.6
-      env:
-        - CXX=clang++-3.6
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-3.7 DISABLE_ASAN=yes
       addons:
         apt:
-          sources:
-            - llvm-toolchain-precise-3.7
-            - ubuntu-toolchain-r-test
+          sources: ["llvm-toolchain-precise-3.7", "ubuntu-toolchain-r-test"]
           packages: clang-3.7
-      env:
-        - CXX=clang++-3.7
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-3.8
       addons:
         apt:
-          sources:
-            - llvm-toolchain-precise-3.8
-            - ubuntu-toolchain-r-test
+          sources: ["llvm-toolchain-precise-3.8", "ubuntu-toolchain-r-test"]
           packages: clang-3.8
-      env:
-        - CXX=clang++-3.8
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-3.9 DISABLE_ASAN=yes
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-3.9
-            - ubuntu-toolchain-r-test
+          sources: ["llvm-toolchain-trusty-3.9", "ubuntu-toolchain-r-test"]
           packages: clang-3.9
-      env:
-        - CXX=clang++-3.9
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-4.0
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-4.0
-            - ubuntu-toolchain-r-test
+          sources: ["llvm-toolchain-trusty-4.0", "ubuntu-toolchain-r-test"]
           packages: clang-4.0
-      env:
-        - CXX=clang++-4.0
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
     - os: linux
-      dist: trusty
+      env: COMPILER=clang++-5.0
       addons:
         apt:
-          sources:
-            - llvm-toolchain-trusty-5.0
-            - ubuntu-toolchain-r-test
+          sources: ["llvm-toolchain-trusty-5.0", "ubuntu-toolchain-r-test"]
           packages: clang-5.0
-      env:
-        - CXX=clang++-5.0
-        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
-        - BUILD_WITH_ASAN=yes
+    - os: linux
+      env: COMPILER=clang++-6.0
+      addons:
+        apt:
+          sources: ["llvm-toolchain-trusty", "ubuntu-toolchain-r-test"]
+          packages: clang-6.0
 
     # macOS/clang
     # https://docs.travis-ci.com/user/osx-ci-environment/#OS-X-Version
     - os: osx
       osx_image: xcode7.3
-      env:
-        - NODE_LABELS="OSX OSX-10.11"
-        - BUILD_WITH_ASAN=yes
+      env: OSX_VERSION=10.11
     - os: osx
       osx_image: xcode8.3
-      env:
-        - NODE_LABELS="OSX OSX-10.12"
-        - BUILD_WITH_ASAN=yes
+      env: OSX_VERSION=10.12
     - os: osx
-      osx_image: xcode9
-      env:
-        - NODE_LABELS="OSX OSX-10.12"
-        - BUILD_WITH_ASAN=yes
+      osx_image: xcode9.2
+      env: OSX_VERSION=10.12
+
+  allow_failures:
+    - env: COMPILER=clang++-6.0
+
+  fast_finish: true
 
 before_script:
+  - if [[ ${TRAVIS_OS_NAME} == linux ]]; then export NODE_LABELS="Linux Ubuntu Ubuntu-14.04"; fi
+  - if [[ ${TRAVIS_OS_NAME} == osx ]]; then export NODE_LABELS="OSX OSX-${OSX_VERSION}"; fi
+  - if [[ -n ${COMPILER} ]]; then export CXX=${COMPILER}; fi
   - ${CXX:-c++} --version
   - python --version