Avoid deadlock by broadcasting outside lock.

We can end up in a rare tangled mess when sending broadcasts while
PackageManager is still trying to deal with scanAvailableAsecs().

Long-term solution is to make Environment.isExternalStorageEmulated()
more robust, but for now we just send these internal broadcasts
after we drop the MountService lock.

Bug: 22858403
Change-Id: I7b43865782f48a679882fd1675b7b961e1292df4