restapi: copy disk - fixing rsdl and SD lookup method

* rsdl:
mandatory arguments - changing to 'storagedomain.id|name'
optional arguments - adding 'action.grace_period.expiry: 'xs:long'

* AbstractBackendActionableResource:
lookupStorageDomainIdByName - using 'GetAllStorageDomains' query
instead of search to allow usage for non-admins.

* BackendTemplateDiskResource:
GetDiskByDiskId query for getting Disk entity.

Change-Id: Ic8bea5e02d1a14599cefbeada241f132df8ccda8
Signed-off-by: Daniel Erez <derez@redhat.com>