retrieval hangs when using IpfsOnlineMode=true

[jsign]

In the context of using Lotus with a go-ipfs node as the underlying blockstore, I've faced what seems to be a bug.
When running with the default [Client] IpfsOnlineMode = false, retrievals works fine, but with true they hang.

If I run with "online"=true, the retrieval hangs with the last retrieval-event being:
retrieval event {"name": "ClientEventLastPaymentRequested", "deal ID": "0", "state": "DealStatusFundsNeededLastPayment", "message": ""}
After that, it simply hangs.
(BTW, that "deal ID": 0 might be another thing to fix, it also prints that on successful retrievals. It isn't the correct Deal ID.)

I came up with a simple way to let anyone reproduce this.

Preparation:

• git clone https://github.com/jsign/lotus && cd lotus && git checkout jsign/onlinefailretrieval && make deps
  (it's based on Lotus master)

Test-flow:

1. docker run -p 5001:5001 --rm --name ipfs ipfs/go-ipfs:v0.7.0
2. go test ./node -race -v -run=TestAPIDealFlow/TestFastRetrievalDealFlow -count 1
3. Wait for the result (PASS or hangs (more on this below)
4. After that, Ctrl+C the docker run ... window, as to clean up things.
   The cloned branch will test a setup with onlineMode := true, so you should see the test hanging.

To check that running in onlineMode := false pass the test, simply change the onlineMode := value in line 406 node/test/builder.go. Nothing else needs to be changed. Then just do Test-Flow steps again.

This is a somewhat modified existing test. It has minimal changes to create this scenario, and reproduce the problem. Obviously, doing git diff with Louts master can show changes.

[jsign]

For our purposes, this problem isn't a high priority anymore since we worked around relying on IpfsOnlineMode=true.