Test: updater.sh update xz-java
Change-Id: I3924b5651f2fac3c5d7493964b570f2f39bc4777

If the upstream is GIT and version is not a hash, updater will try to
list upstream tags to find a newer version. And suggest to merge from
that tag.

Change-Id: I34651815c761c78fd0485df0a84adc086a810e9e
Test: Change googletest/METADATA to follow upstream releases. And run updater.

Add the support to check how far a project is behind upstream git.

Still need to manually run git merge. But this tool can help update
METADATA. :)

Test: ./updater.sh update perf_data_converter
Change-Id: Ic46a0eb723ae22f0fc7d61a67a14299761b564a4