apex: fix selinux denials

We also look to use the loop-control device to identify loop devices.
We only create devices if they don't exist. Modern kernels can have
an option CONFIG_BLK_DEV_LOOP_MIN_COUNT=16 to pre-create the devices.

Change-Id: Ib10cd29f17be4684dd75e0927a2862bf541cd661
3 files changed