Process a single input file with BAM or uniform background.

def _run_cnvkit_single(data, background=None):
    """Process a single input file with BAM or uniform background.
    """
    if not background:
        background = []
    ckouts = _run_cnvkit_shared([data], background)
    if not ckouts:
        return [data]
    else:
        assert len(ckouts) == 1
        return _associate_cnvkit_out(ckouts, [data])