Mock time.sleep to reduce test execution
Mock time.sleep to reduce test execution

In osutils.test_windows, _test_set_network_adapter_mtu
should mock time.sleep when the execution fails,
otherwise the tests will take 3 seconds longer.

This change reduces unit tests execution from ~11s to ~8s.

Change-Id: I02186997d96e766fd2b5adb66e7aa02a4056d97c

stackforge/cloudbase-init