Fix crashes related to unmounting when app on sdcard has an active notification

in status bar.
When unmounting sdcard, all the secure containers have to be unmounted first
before invoking the MountService call back. We send a broadcast
about disabled packages. Force a gc to clean up any stale asset references
 and then unmount the containers before invoking the MountService call back.

Change-Id: I831da1ae54aeec89de3601b94a4a2fae5dc7e495