No camera for idle uids - selinux

If a UID is idle (being in the background for more than
cartain amount of time) it should not be able to use the
camera. If the UID becomes idle we generate an eror and
close the cameras for this UID. If an app in an idle UID
tries to use the camera we immediately generate an error.
Since apps already should handle these errors it is safe
to apply this policy to all apps to protect user privacy.

Test: Pass - cts-tradefed run cts -m CtsCameraTestCases
      Added - CameraTest#testCameraAccessForIdleUid

Change-Id: I9ab3d6ec99764a93638746f18912ed60d299015f