Fix issue #7343719: GlobalActions dialog (power off / airplane mode / sound off)

does not show if you press on power button when the "low battery" dialog is showing up

Always put the global actions dialog in the keyguard dialog layer (above
the keyguard).  I don't see any reason to have it change layers based
on whether the keyguard is showing.

Change-Id: I1bd3600af9f115d662d2a4783f835e234db1b7f0