Fix conversion warning in tablet_server-test.cc
Fix conversion warning in tablet_server-test.cc

Fix tablet_server-test.cc:790:5: warning: converting ‘false’ to pointer
type for argument 1 of ‘char
testing::internal::IsNullLiteralHelper(testing::internal::Secret*)’
[-Wconversion-null]

Change-Id: I7eb730a7b90fc7a703a648d882faebccadf2de9b
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1109
Reviewed-by: Matteo Bertozzi <1d5ca967930bde0bdce795acbf71a5e281d2d4e5@cloudera.com>
Tested-by: jenkins

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