Add SSH logs when provisioning with RedHat derivatives

Fixes #3507

Signed-off-by: KOBAYASHI Shinji <koba@jp.fujitsu.com>

libmachine/provision/redhat_ssh_commander.go

@@ -1,7 +1,10 @@
 package provision
 
 import (
+	"fmt"
+
 	"github.com/docker/machine/libmachine/drivers"
+	"github.com/docker/machine/libmachine/log"
 	"github.com/docker/machine/libmachine/ssh"
 )
 
@@ -15,17 +18,29 @@ func (sshCmder RedHatSSHCommander) SSHCommand(args string) (string, error) {
 		return "", err
 	}
 
+	log.Debugf("About to run SSH command:\n%s", args)
+
 	// redhat needs "-t" for tty allocation on ssh therefore we check for the
 	// external client and add as needed.
 	// Note: CentOS 7.0 needs multiple "-tt" to force tty allocation when ssh has
 	// no local tty.
+	var output string
 	switch c := client.(type) {
 	case *ssh.ExternalClient:
 		c.BaseArgs = append(c.BaseArgs, "-tt")
-		client = c
+		output, err = c.Output(args)
 	case *ssh.NativeClient:
-		return c.OutputWithPty(args)
+		output, err = c.OutputWithPty(args)
 	}
 
-	return client.Output(args)
+	log.Debugf("SSH cmd err, output: %v: %s", err, output)
+	if err != nil {
+		return "", fmt.Errorf(`Something went wrong running an SSH command!
+command : %s
+err     : %v
+output  : %s
+`, args, err, output)
+	}
+
+	return output, nil
 }