Unmount VirtualBox Guest Additions CD from the temp directory.

    CLI Example:

    .. code-block:: bash

        salt '*' vbox_guest.additions_umount

    :param mount_point: directory VirtualBox Guest Additions is mounted to
    :return: True or an string with error

def additions_umount(mount_point):
    '''
    Unmount VirtualBox Guest Additions CD from the temp directory.

    CLI Example:

    .. code-block:: bash

        salt '*' vbox_guest.additions_umount

    :param mount_point: directory VirtualBox Guest Additions is mounted to
    :return: True or an string with error
    '''
    ret = __salt__['mount.umount'](mount_point)
    if ret:
        os.rmdir(mount_point)
    return ret