roomservice: add repo to syncable repo list if dir doesn't exist

breakfast may get stuck if the first breakfast for a target is
interrupted before cloning but after adding repositories to local
manifest. Re-doing breakfast skips syncing the repositories if
they're added to the manifest even if not cloned.

Change-Id: Ifefd08fa6da8785c1d5de0b27ac1a08a782f21d6