Allow for a simple "p4d configuration" mechanism to setup a way for multiple p4ds to be used without having to provide settings like P4PORT, etc via headers.
Right now, you'd set P4DCONFIGDIR to a local directory, and the provide a P4DID either as a default in the configuration or via a header.
I didn't include it in the path or query parameters, because then it would have been required by clients on *every method call* which seemed like the wrong approach. Most clients will interop primarily with a single server, so creating a client object per server didn't seem ridiculous.