Installation of the gpb and protobuffs mocks, in inttest, is now done
using copy in proto_{gpb,protobuffs}_rt:files/0. Previously, rebar
prepare-deps was used, the dependencies had an rsync source with a
relative path back to the inttest directory. This eliminates a
dependency in inttest to rsync, instead relying on retest's
functionality to copy files and directories. Also, it eliminates
hidden knowledge about the directory layout that retest chooses.
Idea and suggestion by Tuncer Ayaz.
Since the dependency sources in the inttest rebar.config files are no
longer used, they are now changed back from rsync paths to git urls,
to serve as examples.
