[build-and-test] add short-circuiting for RUN_FLAKY_ONLY
[build-and-test] add short-circuiting for RUN_FLAKY_ONLY

Added a short circuit into build-and-test.sh: in case of
RUN_FLAKY_ONLY=1 and no flaky tests are reported, don't build
anything and report success right away.

Change-Id: I69278c08c496749cd5f30e2d042b9291efde202c
Reviewed-on: http://gerrit.cloudera.org:8080/12154
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>

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