ci: make unit tests execution compatible with different versions of Boost

This commit also unifies the coding style of CI scripts.

Change-Id: Iae73f63d8a997dbfde9233b6ee7f53a3d9644ef6
Refs: #3750
diff --git a/.travis.yml b/.travis.yml
index 6ed51f3..db62c24 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,18 +7,21 @@
   include:
     - os: linux
       dist: trusty
-      env: CXX=g++
+      env:
+        - CXX=g++
+        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
     - os: linux
       dist: trusty
-      env: CXX=clang++
+      env:
+        - CXX=clang++
+        - NODE_LABELS="Linux Ubuntu Ubuntu-14.04"
     - os: osx
-      env: CXX=clang++
+      env:
+        - CXX=clang++
+        - NODE_LABELS="OSX OSX-10.9"
 notifications:
   email:
     on_success: always
     on_failure: always
 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-10.9"; fi
-  - echo $NODE_LABELS
   - ./.jenkins