HBASE-7689 CloneTableHandler notify completion too early
HBASE-7703 Eventually all online snapshots fail due to Timeout at same regionserver.

Online snapshot attempts would fail due to timeout because a rowlock could not be obtained.  Prior to this a
cancellation occurred which likely grabbed the lock without cleaning it properly. The fix here is to use nice cancel
instead of interrupting cancel on failures.
HBASE-7720  Improve logging messages of failed snapshot attempts.

Improve failed nline snapshot error messages.

Fixed to give better failure error messages.
HBASE-7633 Fix flakey TestZKProcedure.testMultiCohortWithMemberTimeoutDuringPrepare