DO NOT MERGE - FLAG_PRIVILEGED disappears if privileged app is updated and rebooted

Since Kitkat, an app pre-loaded under /system/priv-app/ has
FLAG_PRIVILEGED. However, if the app updated and the device
rebooted, privileged flag is unset from pkgFlags. This patch
fix issue to assign privileged flag when scanning the updated
packages.

Bug: 12640283

Cherrypick from master.

Change-Id: I833d94cd911693c9291e8204f63bd8de945dbba6