core: required space validation - destination domain

LiveMigrateVmDisksCommand -> isValidSpaceRequirements:
add destination domain name to canDoActionMessage
(instead of using getStorageDomain() - prevents a NPE).

Change-Id: I51e0be2ccf541ee435ae04814baeedf3c3373af3
Bug-Url: https://bugzilla.redhat.com/888316
Signed-off-by: Daniel Erez <derez@redhat.com>