JMXHelper in samples lib should select its MBeanServer more carefully

Class JMXHelper selects the MBeanServer in which to install its DynamicMBean by grabbing the first server found in the server factory list or, failing that, using the platform mbean server. It should allow the desired mbean server to be configured and, in the absence of any such configuration, select the platform server. Specifically:

When looking up the mbean server JMXHelper should check System property org.jboss.byteman.jmx.domain-name. If set, it should return the first server in the server factory's list whose domain name (computed by calling getDomaiName()) is equal to the value of this system property. If no server matches or if the property is not set it should return the platform mbean server.

The two MBean scripts in the sample scripts directory should include a note mentioning this configuration option.