pytest: Have bitcoind remember its config file

There were a few places we were rebuilding the config path by appending
`bitcoin.conf` to the bitcoin directory. So now we just remember it and
reference it instead.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

tests/btcproxy.py

@@ -34,8 +34,7 @@ class BitcoinRpcProxy(object):
         self.request_count = 0
 
     def _handle_request(self, r):
-        conf_file = os.path.join(self.bitcoind.bitcoin_dir, 'bitcoin.conf')
-        brpc = BitcoinProxy(btc_conf_file=conf_file)
+        brpc = BitcoinProxy(btc_conf_file=self.bitcoind.conf_file)
         method = r['method']
 
         # If we have set a mock for this method reply with that instead of

tests/utils.py

@@ -305,9 +305,9 @@ class BitcoinD(TailableProc):
         # 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, BITCOIND_REGTEST)
-        self.rpc = SimpleBitcoinProxy(btc_conf_file=btc_conf_file)
+        self.conf_file = os.path.join(bitcoin_dir, 'bitcoin.conf')
+        write_config(self.conf_file, BITCOIND_CONFIG, BITCOIND_REGTEST)
+        self.rpc = SimpleBitcoinProxy(btc_conf_file=self.conf_file)
         self.proxies = []
 
     def start(self):