Fix log shutdown CHECK failure after failed Init()
Fix log shutdown CHECK failure after failed Init()

We need to check whether the Log::Appender's thread_ was allocated and
started before attempting to shut it down.

Change-Id: I76e411c3dcf2789c0c3ec128639e38ca8b2c4bdc
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3874
Tested-by: jenkins
Reviewed-by: Todd Lipcon <2c763d726a8c2f6afda9be7e0e56a2caa6bb5e6b@cloudera.com>

helifu/kudu,andrwng/kudu,helifu/kudu,andrwng/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,cloudera/kudu,cloudera/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,helifu/kudu,helifu/kudu,EvilMcJerkface/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,andrwng/kudu,andrwng/kudu,InspurUSA/kudu,cloudera/kudu,cloudera/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,helifu/kudu,cloudera/kudu,helifu/kudu,InspurUSA/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu