[services-ng] fix bug of connect_timeout in pg_timeout

When there is no connect_timeout in conn_opts, we should use the default value.

Add a new unit test case for connect_timeout

Unit-test passed: warden/non-warden
Yeti-test passed: plan 100/200

Change-Id: I6272b2d42103e93ab8a31ebf9926b91acaf96783