restapi: fix rsdl generation for import glance image

Import action has been missing under
'/api/storagedomains/{storagedomain:id}/images/{images:id}/'.
Hence, added missing signature on ImagesResource interface.

Change-Id: Icf119c8a9b30385d14c756217d5c3c7fead84472
Bug-Url: https://bugzilla.redhat.com/1096496
Signed-off-by: Daniel Erez <derez@redhat.com>