Unmount all asec apps before encrypting

Now that forward locked apps are stored on /data as asec image files
that are mounted, they need to be unmounted before /data can be unmounted
so it can be encrypted.

Change-Id: I7c87deb52aaed21c8ad8ce8aceb7c15c2338620a
Only cleanup ASECs in external storage DO NOT MERGE

Any ASEC or OBB files were unmounted when USB storage was set to UMS
mode. This changes it so only ASEC files on external storage and OBB
files mounted from external storage are unmounted.

(Cherry-pick of 93ecb38daded7583a4a61f4f22519bb7a8a8c154)

Bug: 6948035
Change-Id: Ib60727bd360caa32173797ff5b4e1e21fcf20054
merge in jb-mr0-release history after reset to jb-dev
Merge android-4.1.2_r1