Get a named instance of InputOutput, which represents an output tab in
the output window. The output tab will expose server state management
actions for the given server: start, debug, restart, stop and refresh.
Streams for reading/writing can be accessed via getters on the returned
instance. If the InputOutput already exists for the given server, the
existing instance will be returned. The display name of the given server
will be used as a name for the tab.
url - server instance id (DeploymentManager url).
an InputOutput instance for accessing the new tab,
null if there is no registered server instance with the given url.