threading / start processes using twisted: use ProcessProtocol

[Antoine Martin]

When starting a process and watching its output, we shouldn't do this in a separate thread but instead integrate the code with twisted main-loop (gtk/glib's actually) using ProcessProtocol?, see ​here

Also, when waiting for a process by pid (one we may not have launched ourselves), we should use gobject.child_watch_add(pid) which will also integrate with the main loop.

Places of interest:

• 1 ssh_key_util.generate_new_key: simple call_when_done callback
• 2 config_server.do_tunnel_connect_test: simple call_when_done callback (needs output and returncode)
• 3 ssh_command_monitor: needs every line to be parsed as they are received...
• 4 server_link.do_connect_to_server: re-implements wait_for_socket!!!

[Antoine Martin]

4 was done by r1823: removing the unused code
1 and 2 done in r1830

just leaves 3...