Please tidy up jetty port references in our configuration files

The jetty port is configured, i.e. in jetty.xml it is hard coded to 8181 but that a variable is also used to override the port, i.e:

org.ops4j.pax.web.cfg:org.osgi.service.http.port=8181
system.properties:org.osgi.service.http.port=8181

And in Fabric, the default profile has this set to 0. I believe the fabric one has to say but it would be nice to set this in one place alone and also remove the hard coding in jetty.xml file so it is obvious we are using this field.

Approved from ENH call and planned for 6.3