HostFilter Not Used for Control Connection

[amcrn]

The HostFilter is not being used for the Control Connection (aka the controlConn). This can be problematic, especially if the host is being filtered due to it being in a bad state, as it can hold up the creation of the Control Connection (and therefore the Session itself) for quite some time.

This also fixes an issue if disableControlConn=true and/or DisableInitialHostLookup=true, where the Ring is updated with the host, prior to filtering:

gocql/session.go

Lines 265 to 268 in db6d556

	host := s.ring.addOrUpdate(host)
	if s.cfg.filterHost(host) {
	continue
	}

Closes: #1723