The chameleon boards went down and as a result, label "chameleon" got wiped off from host and hence the tests were not running as auto-server was unable to find the right host to run the test. 

I just restarted chameleons on chromeos1-row5-rack1-host1 and chromeos1-row5-rack2-host1 and ran a test manually which worked fine. 

The tests should now continue to run going forward. 

https://ubercautotest.corp.google.com/afe/#tab_id=view_job&object_id=153726446