Use Project.NameKey in GitRepositoryManager

This simplifies all of the calling sites, where they have a
Project.NameKey on hand and would prefer not to invoke .get() to
convert it into a String.

Change-Id: If661fc07cff542a57af3c28f27ab401ce7b3a656
Signed-off-by: Shawn O. Pearce <sop@google.com>
25 files changed