HBASE-7720 Improve logging messages of failed snapshot attempts.



git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/hbase-7290@1445867 13f79535-47bb-0310-9956-ffa450edef68
HBASE-7633 Fix flakey TestZKProcedure.testMultiCohortWithMemberTimeoutDuringPrepare



git-svn-id: https://svn.apache.org/repos/asf/hbase/branches/hbase-7290@1445868 13f79535-47bb-0310-9956-ffa450edef68