rbd: Return error from rbd_create for message processing

Resolving an error reporting bug introduced by commit id '761491e' which
just took the return of virStorageBackendRBDCreateImage and used it as
the basis for the message generated. This would generate EPERM regardless
of error seen.

src/storage/storage_backend_rbd.c

@@ -484,10 +484,7 @@ static int virStorageBackendRBDCreateImage(rados_ioctx_t io,
                                            char *name, long capacity)
 {
     int order = 0;
-    if (rbd_create(io, name, capacity, &order) < 0)
-        return -1;
-
-    return 0;
+    return rbd_create(io, name, capacity, &order);
 }
 
 static int