tests: sync common testing infrastructure with ndn-cxx and NFD

And upgrade waf to version 2.0.21

Change-Id: Id713e0f3035badd97ca7fc03f76e50085b9a266c
diff --git a/tests/wscript b/tests/wscript
index 32c89f4..19bb8e7 100644
--- a/tests/wscript
+++ b/tests/wscript
@@ -5,11 +5,11 @@
     if not bld.env.WITH_TESTS:
         return
 
-    tmp_path = 'TMP_TESTS_PATH="%s"' % bld.bldnode.make_node('tmp-files')
+    tmpdir = 'UNIT_TESTS_TMPDIR="%s"' % bld.bldnode.make_node('tmp-files')
     bld.program(
         target='../unit-tests',
         name='unit-tests',
         source=bld.path.ant_glob(['*.cpp'] + ['%s/**/*.cpp' % tool for tool in bld.env.BUILD_TOOLS]),
         use=['core-objects'] + ['%s-objects' % tool for tool in bld.env.BUILD_TOOLS],
-        defines=[tmp_path],
+        defines=[tmpdir],
         install_path=None)