tests: fix to work with bitcoind master branch.

E               ConnectionRefusedError: [Errno 111] Connection refused

And in debug.log:

2018-05-17T04:06:35Z Warning: Config setting for -rpcport only applied on regtest network when in [regtest] section.

Unfortunately, current versions including 0.16.1 *ignore* the contents of
a '[regtest]' section, so we need it in *both* places.

Also remove the misleading 'rpcport' initialization which we always
override.

Note that we don't fix this message though:

	2018-05-17T04:06:35Z Config options rpcuser and rpcpassword will soon be deprecated. Locally-run instances may remove rpcuser to use cookie-based auth, or may be replaced with rpcauth. Please see share/rpcuser for rpcauth auth generation.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

tests/utils.py

@@ -15,7 +15,6 @@ BITCOIND_CONFIG = {
     "regtest": 1,
     "rpcuser": "rpcuser",
     "rpcpassword": "rpcpass",
-    "rpcport": 18332,
 }
 
 
@@ -40,10 +39,14 @@ def wait_for(success, timeout=TIMEOUT, interval=0.1):
         raise ValueError("Error waiting for {}", success)
 
 
-def write_config(filename, opts):
+def write_config(filename, opts, regtest_opts=None):
     with open(filename, 'w') as f:
         for k, v in opts.items():
             f.write("{}={}\n".format(k, v))
+        if regtest_opts:
+            f.write("[regtest]\n")
+            for k, v in regtest_opts.items():
+                f.write("{}={}\n".format(k, v))
 
 
 class TailableProc(object):
@@ -240,9 +243,13 @@ class BitcoinD(TailableProc):
             '-logtimestamps',
             '-nolisten',
         ]
+        # For up to and including 0.16.1, this needs to be in main section.
         BITCOIND_CONFIG['rpcport'] = rpcport
+        # For after 0.16.1 (eg. 3f398d7a17f136cd4a67998406ca41a124ae2966), this
+        # needs its own [regtest] section.
+        BITCOIND_REGTEST = {'rpcport': rpcport}
         btc_conf_file = os.path.join(bitcoin_dir, 'bitcoin.conf')
-        write_config(btc_conf_file, BITCOIND_CONFIG)
+        write_config(btc_conf_file, BITCOIND_CONFIG, BITCOIND_REGTEST)
         self.rpc = SimpleBitcoinProxy(btc_conf_file=btc_conf_file)
 
     def start(self):