core: TryBackToAllSnapshots- use filtered disks

TryBackToAllSnapshotsOfVmCommand.canDoAction() filters only the relevant
disks to check, and then passes all the disks to ImagesHandler.

This patch cleans up the usage of the filtered disks so filtering isn't
done twice.

Change-Id: I18edb75723b7f6019864e0fcabde49bdb26b53f1
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: Streamline TryBackToAllSnapshots canDoAction

Refactored TryBackToAllSnapshotsOfVmCommand.canDoAction to be more
readable using the early return pattern and overriding
setActionMessageParameters().

Change-Id: I0c96b782837e3a4eaef5399ca20a2b0738db3370
Signed-off-by: Allon Mureinik <amureini@redhat.com>