Skip some tests if security-group extension is disabled

Below testcases need neutron's security-group extension enabled:
  test_create_port_with_no_securitygroups
  test_update_port_with_security_group_and_extra_attributes
  test_update_port_with_two_security_groups_and_extra_attributes

So this is to skip them if security-group extension is disabled.

Change-Id: I47693f445e41d9ad91af68dd760f1ac37ffb254a
1 file changed