add support for JMXConfiguration to Nexus bundles

if configured, set the appropriate system properties via JSW to enable an RMI registry/JMX server agent to be launched at Nexus bundle start.

This allows monitoring a Nexus bundle remotely via JMX using RMI.
Merge pull request #727 from sonatype/NXCM-4947-nexus-bundle-jmx

NXCM-4947 - add support for JMXConfiguration to Nexus bundles