privacyguard: Share privacy package name between activity stacks

AOSP 4.4 now has a stack supervisor with differents activity stacks for home and focus activities.
Every ActivityStack instance has a ref to this supervisor. Just share the privacy guard package name
throught the supervisor.

Patchset 2: Fix formatting

Change-Id: I5dd75cfa7f5e8b568a4302fce98809ae307c6d52
JIRA: CYAN-2874
Issue: https://jira.cyanogenmod.org/browse/CYAN-2874
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>