mini-cluster: condition on NO_TESTS=0
mini-cluster: condition on NO_TESTS=0

This module will be incorporated into the kudu CLI in the near future, but
for now this patch fixes builds that set NO_TESTS=1.

Our precommit builds don't disable tests, so I tested this by running a
local build with NO_TESTS=1. Without this patch, the build failed while
linking libmini-cluster.so. With it, the build passes.

Change-Id: I195b3ed5ed50dfbe7afb3004182bf02a3bcda31a
Reviewed-on: http://gerrit.cloudera.org:8080/8199
Tested-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>
Tested-by: Kudu Jenkins
Reviewed-by: Alexey Serbin <864f6b82bd94e8dda64141d4274519ee66e0102e@cloudera.com>

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