Clean out the old jobs from the job cache

def clean_old_jobs(opts):
    '''
    Clean out the old jobs from the job cache
    '''
    # TODO: better way to not require creating the masterminion every time?
    mminion = salt.minion.MasterMinion(
                opts,
                states=False,
                rend=False,
                )
    # If the master job cache has a clean_old_jobs, call it
    fstr = '{0}.clean_old_jobs'.format(opts['master_job_cache'])
    if fstr in mminion.returners:
        mminion.returners[fstr]()