MINOR: server: server_find functions: id, name, best_match

MINOR: server: server_find functions: id, name, best_match

This patch introduces three new functions which can be used to find a
server in a farm using different server information:
- server unique id (srv->puid)
- server name
- find best match using either name or unique id

When performing best matching, the following applies:
 - use the server name first (if provided)
 - use the server id if provided
 in any case, the function can update the caller about mismatches
 encountered.