Fix problem with update including id

The update includes the id which is obviously not a field that
can be updated.  I would imagine most services would ignore that,
but it probably isn't good policy.

Partial-bug: #1665495

Change-Id: I6c84b549dae53f91d1662f6e41ea632477c7652c

openstack/resource2.py

@@ -644,6 +644,9 @@ class Resource(object):
         :raises: :exc:`~openstack.exceptions.MethodNotSupported` if
                  :data:`Resource.allow_update` is not set to ``True``.
         """
+        # The id cannot be dirty for an update
+        self._body._dirty.discard("id")
+
         # Only try to update if we actually have anything to update.
         if not any([self._body.dirty, self._header.dirty]):
             return self