Socket based communication between ServerManager and Server

Default communication mechanism between SM and Servers is via stdio, with the ProcessManager routing messages. This should usually be fine, since we use the jboss-stdio lib to capture application usage of stdio and preserve the original streams for our own use. But there is a possibility that an extension module running in the SM or a Server will use JNI, which can pollute the stdio streams. The odds of this are higher in a Server, since extending the capability of the SM with something that needs JNI seems unlikely.

So, we need an option to allow users to configure SM-Server communication via sockets.

Tasks:

1) Put SM-Server communication behind an abstraction
2) Implement stdio-based and socket-based versions of the abstraction
3) Update host.xml schema to include configuration elements for the sockets on both the SM and the Servers.

Note that the SM will need a socket anyway for communication with a remote DomainController, so perhaps this socket could be reused.