Downloads the media dump from the server into your local machine.

    In order to import the downloaded media dump, run ``fab import_media``

    Usage::

        fab prod run_download_media
        fab prod run_download_media:filename=foobar.tar.gz

def run_download_media(filename=None):
    """
    Downloads the media dump from the server into your local machine.

    In order to import the downloaded media dump, run ``fab import_media``

    Usage::

        fab prod run_download_media
        fab prod run_download_media:filename=foobar.tar.gz

    """
    if not filename:
        filename = settings.MEDIA_DUMP_FILENAME
    if env.key_filename:
        ssh = settings.PROJECT_NAME
    else:
        ssh = '{0}@{1}'.format(env.user, env.host_string)
    local('scp {0}:{1}{2} .'.format(
        ssh, settings.FAB_SETTING('SERVER_MEDIA_BACKUP_DIR'), filename))