Return a panel with properties from parents.

def _inherited_panel(panel, base_panels_from_pillar, ret):
    '''Return a panel with properties from parents.'''
    base_panels = []
    for base_panel_from_pillar in base_panels_from_pillar:
        base_panel = __salt__['pillar.get'](base_panel_from_pillar)
        if base_panel:
            base_panels.append(base_panel)
        elif base_panel_from_pillar != _DEFAULT_PANEL_PILLAR:
            ret.setdefault('warnings', [])
            warning_message = 'Cannot find panel pillar "{0}".'.format(
                base_panel_from_pillar)
            if warning_message not in ret['warnings']:
                ret['warnings'].append(warning_message)
    base_panels.append(panel)

    result_panel = {}
    for panel in base_panels:
        result_panel.update(panel)
    return result_panel