[OSJC-128] Provide better connecton creation API

Have this default to "openshift.redhat.com" and add default constructor?  
We could have it check for the OPENSHIFT_BROKER_HOST enviroment var, something like.. 
```
private String serverUrl = System.getenv("OPENSHIFT_BROKER_HOST") != null ? System.getenv("OPENSHIFT_BROKER_HOST") : "openshift.redhat.com";
```
Maybe useful for the folks using the client from a gear itself. 

Also, I think before it checked the express.conf for the server, would we still want to do that?