Retrieve httpPort from MBean when not provided in configuration

The exposed MBean WebSphere/endpoint/channelfw/defaultHttpEndpoint contain Host and Port attributes which could be used if httpPort is not configured in arquillian.xml.

The Container require serverName to detect which VM is running, and as long as you have the VM you have the httpPort info. Defaulting to the 'defaultHttpEndpoint' should remove a few possible error configurations.