This makes it possible to compile on the bots without hardcoding paths
to Ant, Java and ffmpeg deep into the Python scripts (hardcoded paths exists only in the buildbot configuration).
For bots, the ANT_HOME, JAVA_HOME and FFMPEG_HOME environment variables must be set to the install locations for each of these dependencies, for Windows.
This CL also improves the return code handling to make failures easier to detect when things break.
TEST=running build_zxing.py without Ant or Java in the PATH, but with
ANT_HOME, JAVA_HOME and FFMPEG_HOME set. Running Chromium's src/chrome/test/functional/webrtc_video_quality.py.
BUG=none
Review URL: https://webrtc-codereview.appspot.com/1002005
git-svn-id: http://webrtc.googlecode.com/svn/trunk@3311 4adac7df-926f-26a2-2b94-8c16560cd09d
b13dfbffd7