Use TestRepository's Git and Repository in acceptance tests

Avoid storing two references that have to be kept in sync, now that a
Git is available directly from TestRepository. Use a git() convenience
method to AbstractDaemonTest to shorten this. Similarly, add a repo()
convenience method to get the Repository.

Change-Id: I1ec8af8fead0876a2836f7972b5caf603847b25d
17 files changed