[clock] clean up hybrid_clock-test

This patch contains a small clean up on the HybridClockTest:
  * added ASSERT/CHECK for methods returning Status
  * added scoped cleanup into TestClockDoesntGoBackwardsWithUpdates

Change-Id: I1c62cf51e11041b2369d29ff4f714876fd352cea
Reviewed-on: http://gerrit.cloudera.org:8080/14474
Reviewed-by: Adar Dembo <adar@cloudera.com>
Tested-by: Kudu Jenkins
1 file changed