[tests] bind functional test nodes to 127.0.0.1

Prevents OSX firewall allow-this-application-to-accept-inbound-connections
permission popups and is generally safer.

To prevent binding to 127.0.0.1, set self.bind_to_localhost_only = False.

test/functional/test_framework/test_node.py

@@ -16,6 +16,7 @@ import time
 
 from .authproxy import JSONRPCException
 from .util import (
+    append_config,
     assert_equal,
     get_rpc_proxy,
     rpc_url,
@@ -42,7 +43,7 @@ class TestNode():
     To make things easier for the test writer, any unrecognised messages will
     be dispatched to the RPC connection."""
 
-    def __init__(self, i, dirname, extra_args, rpchost, timewait, binary, stderr, mocktime, coverage_dir, use_cli=False):
+    def __init__(self, i, dirname, rpchost, timewait, binary, stderr, mocktime, coverage_dir, extra_conf=None, extra_args=None, use_cli=False):
         self.index = i
         self.datadir = os.path.join(dirname, "node" + str(i))
         self.rpchost = rpchost
@@ -57,6 +58,8 @@ class TestNode():
             self.binary = binary
         self.stderr = stderr
         self.coverage_dir = coverage_dir
+        if extra_conf != None:
+            append_config(dirname, i, extra_conf)
         # Most callers will just need to add extra args to the standard list below.
         # For those callers that need more flexibity, they can just set the args property directly.
         # Note that common args are set in the config file (see initialize_datadir)