Disable ChannelManagerTest.StartupShutdownOnUnstartedThread
The test is testing a scenario that shouldn't happen.

BUG=3388
TBR=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/21509005

git-svn-id: http://webrtc.googlecode.com/svn/trunk@6238 4adac7df-926f-26a2-2b94-8c16560cd09d