android: Filter host tools out of PATH.

When running actions/rules we need to filter the Android host tools out
of the PATH because they include some tools that are not suitable for
being executed outside of the normal Android build rules (like a custom
version of bison).
Review URL: https://codereview.chromium.org/12016019

git-svn-id: http://gyp.googlecode.com/svn/trunk@1564 78cadc50-ecff-11dd-a971-7dbc132099af