lnd: use asynchronous streaming responses for [open|close]channel RPC's

This commit switches the implementation of the open/close channel RPC’s
from a fully blocking synchronous model to one that’s async by default,
allowing callers to add a sync wrapper.

The new proto specs also allow for “updates” for the pending channels
in the form of new confirmations which progress the pending status of
the channel. At this point, only the final open/close updates have been
implemented. Obtaining confirmation notifications requires a bit of
re-working within the current ChainNotifier interface, thus this has
been deferred to a later time.

server.go

@@ -256,6 +256,7 @@ type closeChanReq struct {
 // closeChanResp is the response to a closeChanReq is simply houses a boolean
 // value indicating if the channel coopertive channel closure was succesful or not.
 type closeChanResp struct {
+	txid    *wire.ShaHash
 	success bool
 }
 
@@ -437,7 +438,7 @@ func (s *server) ConnectToPeer(addr *lndc.LNAdr) (int32, error) {
 // OpenChannel sends a request to the server to open a channel to the specified
 // peer identified by ID with the passed channel funding paramters.
 func (s *server) OpenChannel(nodeID int32, localAmt, remoteAmt btcutil.Amount,
-	numConfs uint32) (*wire.OutPoint, error) {
+	numConfs uint32) (chan *openChanResp, chan error) {
 
 	errChan := make(chan error, 1)
 	respChan := make(chan *openChanResp, 1)
@@ -451,17 +452,14 @@ func (s *server) OpenChannel(nodeID int32, localAmt, remoteAmt btcutil.Amount,
 		resp: respChan,
 		err:  errChan,
 	}
+	// TODO(roasbeef): hook in "progress" channel
 
-	if err := <-errChan; err != nil {
-		return nil, err
-	}
-
-	return (<-respChan).chanPoint, nil
+	return respChan, errChan
 }
 
 // CloseChannel attempts to close the channel identified by the specified
 // outpoint in a coopertaive manner.
-func (s *server) CloseChannel(channelPoint *wire.OutPoint) (bool, error) {
+func (s *server) CloseChannel(channelPoint *wire.OutPoint) (chan *closeChanResp, chan error) {
 	errChan := make(chan error, 1)
 	respChan := make(chan *closeChanResp, 1)
 
@@ -472,11 +470,7 @@ func (s *server) CloseChannel(channelPoint *wire.OutPoint) (bool, error) {
 		err:  errChan,
 	}
 
-	if err := <-errChan; err != nil {
-		return false, err
-	}
-
-	return (<-respChan).success, nil
+	return respChan, errChan
 }
 
 // Peers returns a slice of all active peers.