appops: do not prune apps that are not present

Do not prune apps that are not currently present in the device (like sdcards ones). During
booting sdcards are not available but must not be purge from appops, because they are still
present in the android app database.
JIRA: CYAN-2811
Issue: https://jira.cyanogenmod.org/browse/CYAN-2811

Change-Id: I1a7a6510eb80e8246265f53520dc9020c02a31f5
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
Merge "appops: do not prune apps that are not present" into pac-4.4