Instead of hardcoding one server, let the connection manager try doing
SRV resolution and if the resolution fails, let it try a list of fallback
servers. Note that talkx.l.google.com is now used instead of
talk.google.com. This is the DNS used in the Windows client, this DNS
returns a list of IPs instead of 1. This also enable usage of HTTPS
proxy when falling back to port 443 with old_ssl.

Reviewed-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>