[tools] Fail ksck if fetching consensus state fails
[tools] Fail ksck if fetching consensus state fails

Commonly, users run ksck as someone other than the kudu superuser.
This means that ksck can't gather consensus state. It still does its
other checks, and will exit with an OK status if there are no
problems with them, just printing some easily-missed warnings at
the top of the output. This patch changes ksck so it fails when
it cannot gather all the information it needs to do all the checks.

Note that if the user specifies consensus=false, they can run ksck
without missing consensus checks causing a failure.

Change-Id: Id3efc9342c3cb3f9652bb8c9789fe20ecf12ff55
Reviewed-on: http://gerrit.cloudera.org:8080/9316
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>
Tested-by: Kudu Jenkins

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