[winswitch] Proper way of determining when an XPRA server is ready

[Timothy Hobbs]

What is the proper way of programatically finding out if the XPRA server 
is ready for clients to connect to it?

Right now, subuser waits for the xpra socket to exist, but apparently 
that doesn't work.

https://github.com/subuser-security/subuser/issues/224

Is waiting for the xpra server to write |"||xpra is ready." a valid method?

|Basically, what subuser does, is it first launches xpra server in a 
container, then it launches xpra client in a container, and then it 
launches an application in a third container and gives that application 
access to the xpra server's x11 server.

Thanks for your advice,

Timothy Hobbs - author of subuser