Enable batch rpc processing

* Can be exercised from the command line with json2

* Rewrite Env::do_rpc to call the same code as
  rpc from the command line.  This puts rpc
  handling logic in one place.

src/test/server/ServerStatus_test.cpp

@@ -786,7 +786,7 @@ class ServerStatus_test :
         using namespace beast::http;
         Env env {*this, validator( envconfig([](std::unique_ptr<Config> cfg)
             {
-                cfg->section("port_rpc").set("protocol", "http,https");
+                cfg->section("port_rpc").set("protocol", "http");
                 return cfg;
             }), "")};