[tests] fix hybrid_clock-test

I noticed HybridClockTest.AutoTimeSourceNoDedicatedNtpServer was failing
from time to time on AWS instances.  It turned out the scenario missed
setting of the fake DNS server, but the comments claimed it did.

This patch addresses the issue.

Change-Id: I1386646d592eb0d127a6a216664c6f241c316c6d
Reviewed-on: http://gerrit.cloudera.org:8080/18928
Reviewed-by: Attila Bukor <abukor@apache.org>
Tested-by: Alexey Serbin <alexey@apache.org>
1 file changed