Add MountService tests and fix a bug it found

Add some MountService tests that are based partially on some stuff done
in PackageManagerTests. This allows us to test the OBB changes in an
easy way.

Also, it found some bugs in the DefaultContainerService connection state
machine, so fix those while we're at it.

Change-Id: I18f38593be754eb32fb6e842f88eec47e2beefce