core: Remove unused ImagesHandlerActionParameters

Change-Id: I15e2ed654331b812a41c6bd68d4a42d4f3077961
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: Remove checkImagesLocked(vmId, messages)

Removed ImagesHandler.checkImagesLocked(Guid vmId, List<String
messages), as ImagesHandler should not know about VMs.

Wherever it was used (two places - AddVmFromSnapshot and
LiveMigrateVmDisks), it was replaced with a direct call to DiskDao and
then a simpler call to
ImagesHandler.checkImagesLocked (messages, disks).

Change-Id: Iae603af05f4b90e8c021113779031846a56c99ff
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: Remove image status check from ImagesHandler

Extracted all image status checks from ImagesHandler and moved them to
the new DiskImagesValidator class, as a step in the effort to decouple
ImagesHandler.PerformImagesChecks.

Change-Id: I7c26d6cf37227aded9318523f0a807e19eeaa7bc
Signed-off-by: Allon Mureinik <amureini@redhat.com>