Mount/Unmount secure containers

Persist flags in PackageSetting. Flags are relevant to ApplicationInfo.FLAG_SYSTEM, Application.FLAG_ON_SDCARD, ApplicationInfo.FLAG_FORWARD_LOCK.
New pm command to simulate mount/unmount in Pm. This will be removed
when MountService/vold event generation gets fixed.
Calls from MountService into PackageManager when media gets mounted/unmounted.
Scan the packages and grant permissions when the sdcard gets mounted.
This api might change again.