Add command line arguments as server subparser.

def add_subparser(subparsers):
    """Add command line arguments as server subparser.
    """
    parser = subparsers.add_parser("server", help="Run a bcbio-nextgen server allowing remote job execution.")
    parser.add_argument("-c", "--config", help=("Global YAML configuration file specifying system details."
                                                "Defaults to installed bcbio_system.yaml"))
    parser.add_argument("-p", "--port", help="Port to listen on (default 8080)",
                        default=8080, type=int)
    parser.add_argument("-n", "--cores", help="Cores to use when processing locally when not requested (default 1)",
                        default=1, type=int)
    parser.add_argument("-d", "--biodata_dir", help="Directory with biological data",
                        default="/mnt/biodata", type=str)
    return parser