test: [move-only] Extract create_new_rpc_connection

Re-using the same rpc connection on multiple threads is obviously
unsafe, so this helper can be used to create one connection per thread.

This refactor does not change any behavior and can be reviewed with the
git options:

--color-moved=dimmed-zebra --color-moved-ws=ignore-all-space

test/functional/test_framework/test_node.py

@@ -301,6 +301,17 @@ class TestNode():
         if self.start_perf:
             self._start_perf()
 
+    def create_new_rpc_connection(self):
+        """Create an additional RPC connection, likely to be used in a new thread."""
+        rpc = get_rpc_proxy(
+            rpc_url(self.datadir_path, self.index, self.chain, self.rpchost),
+            self.index,
+            timeout=self.rpc_timeout // 2,  # Shorter timeout to allow for one retry in case of ETIMEDOUT
+            coveragedir=self.coverage_dir,
+        )
+        rpc.auth_service_proxy_instance.reuse_http_connections = self.reuse_http_connections
+        return rpc
+
     def wait_for_rpc_connection(self, *, wait_for_import=True):
         """Sets up an RPC connection to the bitcoind process. Returns False if unable to connect."""
         # Poll at a rate of four times per second
@@ -322,13 +333,7 @@ class TestNode():
                 raise FailedToStartError(self._node_msg(
                     f'bitcoind exited with status {self.process.returncode} during initialization. {str_error}'))
             try:
-                rpc = get_rpc_proxy(
-                    rpc_url(self.datadir_path, self.index, self.chain, self.rpchost),
-                    self.index,
-                    timeout=self.rpc_timeout // 2,  # Shorter timeout to allow for one retry in case of ETIMEDOUT
-                    coveragedir=self.coverage_dir,
-                )
-                rpc.auth_service_proxy_instance.reuse_http_connections = self.reuse_http_connections
+                rpc = self.create_new_rpc_connection()
                 rpc.getblockcount()
                 # If the call to getblockcount() succeeds then the RPC connection is up
                 if self.version_is_at_least(190000) and wait_for_import: