Add new method call back in MountService.

PackageManager invokes this call back when its done handling
the media status update.
Add new uid check for updateExternalMediaStatus
Change killPids method in ActivityManager.
Remove mountsd command in Pm.java We cannot arbitrarily enable/disable
packages in PackageManager now.

Change-Id: I28dcba4afd2b4486f68abdaa1628a31b66544c91