Only kill apps with storage app data isolation enabled

Only kill apps with storage app data isolation enabled

Originally it kills all the apps with obb and data mounted.
Due to recent changes, all apps will have obb and data dirs mounted
in default root namespace. Hence all apps will be killed by
by KillProcessesWithMounts().

To fix this, we also check if the dir is mounted as tmpfs,
as the default namespace one is bind mounted to lowerfs,
which app data isolation is mounted as tmpfs, so we only
kill the process that have obb dir mounted as tmpfs.

Bug: 148049767
Test: Able to boot without warnings / errors
Ignore-AOSP-First: Merge it along with other CLs, will cherry-pick to
AOSP afterwards.

Change-Id: I45d9a63ed47cbc27aebb63357a43f51ad62275db