Older Twisted (18.4.0) returns TimeoutError instead of
ConnectingCancelledError when connection times out.
This change allows tests to be compatible with this behaviour.
Signed-off-by: Oleg Girko <ol@infoserver.lv>
We need to do a bit more validation when we get a server name, but don't want
to be re-doing it all over the shop, so factor out a separate
parse_and_validate_server_name, and do the extra validation.
Also, use it to verify the server name in the config file.
Make sure that server_names used in auth headers are sane, and reject them with
a sensible error code, before they disappear off into the depths of the system.
