client-test: add some ASSERTs
client-test: add some ASSERTs

Surely an ASSERT failure is better than:

  runtime error: member call on null pointer of type 'kudu::master::Master'

Change-Id: Ic5496d5d502591c17a3e4a0a24ba5d82bcac2e92
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/6314
Tested-by: jenkins
Reviewed-by: Jean-Daniel Cryans <4bf4c125525b8623ac45dfd7774cbf531df19085@cloudera.com>

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