sync: Add manifest_name parameter

This parameter changes the manifest used by 'repo sync' for only
this execution. It should be useful for developers wishing to get
the repo temporarily into a known state, without clobbering their
existing manifest.

Tested by shifting Chrome OS between minilayout and full, and
between several release-builder-generated manifests.

Change-Id: I14194b665195b0e78f368d9ec8b8a83227af2627
1 file changed