Making the tests more robust

[chatman]

1. Instead of waiting 10sec, check the list of live nodes from ZK (/live_nodes znode). You can use the CloudSolrClient's ZK client to check for the cluster state / live nodes.
2. When any command terminates with error (exit code != 0), then don't perform further steps and exit your test with non-0 error code (System.exit(errorCode));
3. Start ZK from the test itself, and on a random port.
4. Use random directory names and random port numbers every time.
5. If there's a success, stop zk, solr and clean up directories.
6. If there's a failure, then don't stop ZK or Solr or cleanup, but instead print the port numbers where things are running and the directories (so that user can manually check the logs in those directories).

[viveknarang]

Agree Ishan !!! Working on them :)