[CX] start cluster script does not throw any message if cluster is already running.

1. start the cluster using start script.
2. Log out.
3. Log back in.
4. Rerun the start script:
./samples/local/bin/start-sample-cluster.sh
java version "1.8.0_45"
Java(TM) SE Runtime Environment (build 1.8.0_45-b14)
Java HotSpot(TM) 64-Bit Server VM (build 25.45-b02, mixed mode)
CLUSTERDIR=/root/cbas-install/samples/local
INSTALLDIR=/root/cbas-install
Waiting for cluster to start..done

Sometimes the above process just hangs intermittently.