Display failing activate/deactivate commands in error dialogs

As was done with a failed mount operation, include the failed activate/
deactivate command in the error dialog.  Two example error dialogs now
look like this:

    (-) Could not deactivate swap

        # swapoff -v /dev/sdb7
        swapoff: /dev/sdb7: swapoff failed: Invalid argument

                                                    [  OK  ]

    (-) Could not unmount /dev/sdb6

        # umount -v "/mnt/6"
        umount: /mnt/6: not mounted

                           [  OK  ]