Refactor PushOp to use Project.NameKey

Elsewhere we keep track of a project by its NameKey object, rather
than a simple String.  Do the same in PushOp, as it makes the API
a bit more clear.

Change-Id: Ieb3120e655b7b1dc43a675555ea8de63900d13a8
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed