VarnishQueue connect only when needed.

[georgir]

Currently VarnishQueue connects immediately, and keeps the connection open forever. Even if you call end() to close the client, reconnect function is bound on the client's close event so it will always keep a connection open.
One unneeded connection may not be a big deal in general, but at the very least it prevents node from exiting.
A better implementation would keep the VarnishClient disconnected while the queue is empty, and reconnect only when needed.