Enable one disabled tests in NEC plugin that blocked by 1229954

Enable the disabled tests in NEC plugin that blocked by 1229954
https://github.com/openstack/neutron/blob/master/neutron
/tests/unit/nec/test_security_group.py#L64

Change-Id: Id15c5b431773d05f13201cdcd126ff2fa9f6aa06
Related-Bug: #1229954
Merge "Enable one disabled tests in NEC plugin that blocked by 1229954"