tests: Expand HTTP coverage to assert libevent behavior

Covers:
- http pipelining
- rpcservertimeout

  Testing this requires adding an option to TestNode to force
  the test framework to establish a new HTTP connection for
  every RPC. Otherwise, attempting to reuse a persistent connection
  would cause framework RPCs during startup and shutdown to fail.

- "chunked" Transfer-Encoding

test/functional/test_framework/authproxy.py

@@ -75,6 +75,7 @@ class AuthServiceProxy():
         self.__service_url = service_url
         self._service_name = service_name
         self.ensure_ascii = ensure_ascii  # can be toggled on the fly by tests
+        self.reuse_http_connections = True
         self.__url = urllib.parse.urlparse(service_url)
         user = None if self.__url.username is None else self.__url.username.encode('utf8')
         passwd = None if self.__url.password is None else self.__url.password.encode('utf8')
@@ -92,6 +93,8 @@ class AuthServiceProxy():
             raise AttributeError
         if self._service_name is not None:
             name = "%s.%s" % (self._service_name, name)
+        if not self.reuse_http_connections:
+            self._set_conn()
         return AuthServiceProxy(self.__service_url, name, connection=self.__conn)
 
     def _request(self, method, path, postdata):
@@ -102,6 +105,8 @@ class AuthServiceProxy():
                    'User-Agent': USER_AGENT,
                    'Authorization': self.__auth_header,
                    'Content-type': 'application/json'}
+        if not self.reuse_http_connections:
+            self._set_conn()
         self.__conn.request(method, path, postdata, headers)
         return self._get_response()