Mock up time.sleep to avoid unnecessary wait in test_ovs_tunnel

Unnecessary wait in ovs tunnel UT introduces extra 6 seconds time cost,
and makes 3 test_daemon_loop cases the slowest tests. Mock up time.sleep
to reduce UT time, from around 6.272s to 0.135s.

Closes-bug: #1401457

Change-Id: Ic0a968a400268af1f66c91e4c39e7d3acf492ef3
Merge "Mock up time.sleep to avoid unnecessary wait in test_ovs_tunnel"