[MINOR] stats: report numerical process ID, proxy ID and server ID

[MINOR] stats: report numerical process ID, proxy ID and server ID

It is very convenient for SNMP monitoring to have unique process ID,
proxy ID and server ID. Those have been added to the CSV outputs.
The numbers start at 1. 0 is reserved. For servers, 0 means that the
reported name is not a server name but half a proxy (FRONTEND/BACKEND).

A remaining hidden "-" in the CSV output has been eliminated too.