Fix SSH issue with in place upgrades. (#247)

The master in-place upgrade is currently broken due to an SSH failure
with the error "Host key verification failed."
As the master machine may change, it should be safe to disable the host
key check, which fixes the issue.

cloud/google/ssh.go

@@ -108,7 +108,7 @@ func (gce *GCEClient) remoteSshCommand(cluster *clusterv1.Cluster, machine *clus
 	}
 
 	command := fmt.Sprintf("%s", cmd)
-	c := exec.Command("ssh", "-i", gce.sshCreds.privateKeyPath, "-q", gce.sshCreds.user+"@"+publicIP, command)
+	c := exec.Command("ssh", "-o", "StrictHostKeyChecking=no", "-o", "UserKnownHostsFile=/dev/null", "-i", gce.sshCreds.privateKeyPath, "-q", gce.sshCreds.user+"@"+publicIP, command)
 	out, err := c.CombinedOutput()
 	if err != nil {
 		return "", fmt.Errorf("error: %v, output: %s", err, string(out))