public static PeerId parsePeer(final String s) {
        final PeerId peer = new PeerId();
        if (peer.parse(s)) {
            return peer;
        }
        return null;
    }
Parse a peer from string in the format of "ip:port:idx",
returns null if fail to parse.

@param s input string with the format of "ip:port:idx"
@return parsed peer
jraft-core/src/main/java/com/alipay/sofa/jraft/entity/PeerId.java