Verify migration type is supported VSMigrationService.
Verify migration type is supported VSMigrationService.

The check call doesn't verify that type supplied is one of the values we support.  Also, allow for NULL in get_migration_type().

Signed-off-by: Kaitlin Rupert <5d963ff58691ce861c80ea2b0deed9b0b88171bc@us.ibm.com>

libvirt/libvirt-cim,libvirt/libvirt-cim,libvirt/libvirt-cim