test: quell warning in disk_failure-itest
test: quell warning in disk_failure-itest

disk_failure-itest will yield the following warning when built:

../../src/kudu/integration-tests/disk_failure-itest.cc:246:3: warning: control may reach end of non-void function [-Wreturn-type]

Change-Id: If9cd6beb9855b0d22cf5fbb74c4d253ff84f4bca
Reviewed-on: http://gerrit.cloudera.org:8080/11385
Tested-by: Kudu Jenkins
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>

InspurUSA/kudu,helifu/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,helifu/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu,InspurUSA/kudu