Handle gracefully situations when MBeans are not available

[joerghoh]

In many cases we have situations where 2 different processes interfere:

• Instantiation of the MBeanStatusProvider based on the config nodes
• Startup of the jmx-extension bundle.

In case the config is handled first, it requires MBeans which are not there yet, resulting in errors and there's no recovery possible.

Therefor I will modify the MBeanStatusProvider like this:

• The creation of the connection to the MBean will be moved off the activator.
• on every call of getStatus() all check for the availability of the mbean will be triggered. If the MBean is not available, it will return "UNKNOWN".