xserver: Ensure that connectToProxy closes.
xserver: Ensure that connectToProxy closes.

If the server is retrying in resolveToEndpoint during shutdown,
we take forever to shutdown. We fix this by using a context to
cancel this loop and all calls it may make.

Change-Id: I3bc22fa34dad3ab805b4f3e157db3bb713820a5e

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref