Do not tolerate malformed RPC/action references in requests URL

RFC8040 parsing of request URI takes RPCs and actions into account silently translating them to NodeIdentifier steps and not stopping there.

This ends up potentially allowing for weird request state being produced, causes some amount of inefficiency and does not give us the tools needed for solving NETCONF-818.

Tighten up parsing so that any RPC or action is treated as a terminal token, not allowing further request elements to be present.