KUDU-1941: more validation for RPC auth flags
KUDU-1941: more validation for RPC auth flags

With this patch, both master and tserver refuse to start if
authentication is 'required' but no authentication method is configured.

Prior to this patch, the inconsistency with the run-time configuration
could be detected at a later stage when a client would try to connect
to Kudu cluster.

Change-Id: I3c088fd6d7a695234e2955e09ca53626078b4e51
Reviewed-on: http://gerrit.cloudera.org:8080/6851
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Kudu Jenkins

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