PackageManagerTests was trying to mount and unmount the media without
waiting for the correct state to arrive. It was proceeding with any
state transition.
Some tests had their own volume mounting and unmounting code that was
flawed, so switch it to the more robust mountMedia() and unmountMedia()
implementations.
Change-Id: If464927bb09dd15cb040c6cce195a6ad8452de95
d7b421b4de