Add to or create a new variable in the make.conf

    Return a dict containing the new value for variable::

        {'<variable>': {'old': '<old-value>',
                        'new': '<new-value>'}}

    CLI Example:

    .. code-block:: bash

        salt '*' makeconf.append_var 'LINGUAS' 'en'

def append_var(var, value):
    '''
    Add to or create a new variable in the make.conf

    Return a dict containing the new value for variable::

        {'<variable>': {'old': '<old-value>',
                        'new': '<new-value>'}}

    CLI Example:

    .. code-block:: bash

        salt '*' makeconf.append_var 'LINGUAS' 'en'
    '''
    makeconf = _get_makeconf()

    old_value = get_var(var)

    # If var already in file, add to its value
    if old_value is not None:
        appended_value = '{0} {1}'.format(old_value, value)
        __salt__['file.sed'](makeconf, '^{0}=.*'.format(var),
                             '{0}="{1}"'.format(var, appended_value))
    else:
        _add_var(var, value)

    new_value = get_var(var)
    return {var: {'old': old_value, 'new': new_value}}