[KNIFE-498] knife rackspace uses direct TCP connection on port 22 to verify SSHD

This adds two options: to disable the TCP check on port 22, and to wait/sleep before doing the TCP check. I decided to call the option ssh_wait_timeout as it needs to sleep *before* the tcp check.

If you're using a ProxyCommand or any other kind of ssh gateway, the SSHD wait no longer works using the method at:

https://github.com/opscode/knife-rackspace/blob/master/lib/chef/knife/rackspace_server_create.rb#L237-239

Since knife bootstrap can use ssh gateways, the TCP check doesn't really model what would happen with knife bootstrap's communication to the server.