unix.sh is shared by multiple OSes and environments. Clear JAVA_HOME,
since we never want to use that as PATH is more reliable, better
supported, and more typical.
Previously, only Windows had the plumbing to rename test results for
the Kokoro result viewers to pretty-print.
macos.cfg was the only CI that lacked a corresponding .sh, which maked
unix.sh harder to reason about. Created macos.sh so that unix.sh is now
just a helper script and will not be called directly by Kokoro.
We now avoid "gradle clean" to avoid wiping results. Still clean compiler
since we do re-run the build multiple times with varying platforms.
Shouldn't be necessary, but "just in case" since I want this commit to
be low risk. This improves Windows to produce detailed results even
if the CI was successful.
Eric Anderson