Retrieve tabix command, handling new bcftools tabix and older tabix.

def get_tabix_cmd(config):
    """Retrieve tabix command, handling new bcftools tabix and older tabix.
    """
    try:
        bcftools = config_utils.get_program("bcftools", config)
        # bcftools has terrible error codes and stderr output, swallow those.
        bcftools_tabix = subprocess.check_output("{bcftools} 2>&1; echo $?".format(**locals()),
                                                 shell=True).decode().find("tabix") >= 0
    except config_utils.CmdNotFound:
        bcftools_tabix = False
    if bcftools_tabix:
        return "{0} tabix".format(bcftools)
    else:
        tabix = config_utils.get_program("tabix", config)
        return tabix