Split merger and launcher git roots

In case a user runs a merger and a launcher on the same host, make
sure that they don't share a git directory (used by the launcher's
internal merger).  They could end up colliding.

Incidentally, that's basically the configuraton used in tests, so
update the test configuration likewise.

Change-Id: I64a690c706d00583973bd2d542a5f42ae6e9ef36
7 files changed