Added parameters to skip host checking when going through an ssh_gateway.

Fixes #11836

If you are using an ssh_gateway and you haven't yet connected to it or accepted the public key (no entry for ssh_gateway in ~/.ssh/known_hosts), then provisioning a minion will hang.  This fix will bypass host checking both when connecting to the ssh_gateway/bastion AND connecting to the target minion (using the ProxyCommand ssh option).