Disable password authentication in SSH command

This will turn off the password authentication prompt which some SSH
commands experience if there is a lag between when we attempt the first
SSH command and the key has been loaded on the server.

Signed-off-by: Nathan LeClaire <nathan.leclaire@gmail.com>

ssh/client.go

@@ -47,6 +47,7 @@ const (
 
 var (
 	baseSSHArgs = []string{
+		"-o", "PasswordAuthentication=no",
 		"-o", "IdentitiesOnly=yes",
 		"-o", "StrictHostKeyChecking=no",
 		"-o", "UserKnownHostsFile=/dev/null",