Fix requery behaviour of MemoryCursor.

As we can't restore the contents of the cursor window, we need to keep
it on deactivation so we can restore it on requery().

Change-Id: I06f688bbe9120c307bdc3ddbc3833416becdec82
FileUtils: add method to get UUID of a volume

Change-Id: I41b76c5e01c82a2f8e67b33133a76947877a2814