Make it works with HipChat Beta

The previous check was bogus when using HipChat Beta (i.e. running
my personal instance of HipChat).
Actually what we're looking after here is if the message is intended
to be sent to a chatroom or to a user.
Chatroom's JID starts with 'conf.', hence the check.

Note that I've tested it on HipChat Beta but not on HipChat On Demand (e.g. hosted version of HipChat)