OBB: rearrange to be entirely asynchronous

Rearrange structure of MountService handling of OBBs to be entirely
asynchronous so we don't rely on locking as much. We still need the
locking to support dumpsys which has been improved to output all the
data structures for OBBs.

Added more tests to cover more of the error return codes.

Oh and fix a logic inversion bug.

Change-Id: I34f541192dbbb1903b24825889b8fa8f43e6e2a9