ARQ-1749 Retrieve httpPort from MBean when not provided in configuration

Reviewed the exceptions; 

- the MalformedObjectNameException in line 346 is only based on the code and reports wrong syntax, not whether the MBean actually exists. If this happens, it's a problem with the code that can currently not be configured.
- the registration error in line 360 is only thrown as a nested exception of the next one
- the general exception in 366 I've enhanced as you can see in line 368

Please let me know whether this commit addresses your concerns.