multi: change NewBitcoindBackend to take a miner as its param

Prepares for the following commit where we assert the chain backend is
synced to the miner.

chainntnfs/bitcoindnotify/bitcoind_test.go

@@ -179,7 +179,7 @@ func testHistoricalConfDetailsTxIndex(t *testing.T, rpcPolling bool) {
 	)
 
 	bitcoindConn := unittest.NewBitcoindBackend(
-		t, unittest.NetParams, miner.P2PAddress(), true, rpcPolling,
+		t, unittest.NetParams, miner, true, rpcPolling,
 	)
 
 	hintCache := initHintCache(t)
@@ -279,7 +279,7 @@ func testHistoricalConfDetailsNoTxIndex(t *testing.T, rpcpolling bool) {
 	miner := unittest.NewMiner(t, unittest.NetParams, nil, true, 25)
 
 	bitcoindConn := unittest.NewBitcoindBackend(
-		t, unittest.NetParams, miner.P2PAddress(), false, rpcpolling,
+		t, unittest.NetParams, miner, false, rpcpolling,
 	)
 
 	hintCache := initHintCache(t)

chainntnfs/test/test_interface.go

@@ -1932,7 +1932,7 @@ func TestInterfaces(t *testing.T, targetBackEnd string) {
 		case "bitcoind":
 			var bitcoindConn *chain.BitcoindConn
 			bitcoindConn = unittest.NewBitcoindBackend(
-				t, unittest.NetParams, p2pAddr, true, false,
+				t, unittest.NetParams, miner, true, false,
 			)
 			newNotifier = func() (chainntnfs.TestChainNotifier, error) {
 				return bitcoindnotify.New(
@@ -1944,7 +1944,7 @@ func TestInterfaces(t *testing.T, targetBackEnd string) {
 		case "bitcoind-rpc-polling":
 			var bitcoindConn *chain.BitcoindConn
 			bitcoindConn = unittest.NewBitcoindBackend(
-				t, unittest.NetParams, p2pAddr, true, true,
+				t, unittest.NetParams, miner, true, true,
 			)
 			newNotifier = func() (chainntnfs.TestChainNotifier, error) {
 				return bitcoindnotify.New(