It seems p2p-compactblocks.py fails randomly

From: https://travis-ci.org/bitcoin/bitcoin/jobs/163788152 from #8841
The PR is trivial and totally unrelated to compact block

```
p2p-compactblocks.py:
Initializing test directory /tmp/test3yd_2q3h/2
start_node: bitcoind started, waiting for RPC to come up
start_node: RPC succesfully started
MiniNode: Connecting to Bitcoin Node IP # 127.0.0.1:11016
Testing SENDCMPCT p2p message... 
Testing compactblock headers and shortIDs are correct...
Assertion failed: 
Stopping nodes
Not cleaning up dir /tmp/test3yd_2q3h/2
Failed
stderr:
  File "/home/travis/build/bitcoin/bitcoin/qa/rpc-tests/test_framework/test_framework.py", line 151, in main
    self.run_test()
  File "/home/travis/build/bitcoin/bitcoin/build/../qa/rpc-tests/p2p-compactblocks.py", line 614, in run_test
    self.test_compactblock_construction()
  File "/home/travis/build/bitcoin/bitcoin/build/../qa/rpc-tests/p2p-compactblocks.py", line 264, in test_compactblock_construction
    assert(self.test_node.last_cmpctblock is not None)
Pass: False, Duration: 7 s
```

MaybeSetPeerAsAnnouncingHeaderAndIDs(nodestate, pfrom, connman);
                        
                        vGetData[0] = CInv(MSG_CMPCT_BLOCK, vGetData[0].hash);
                    }
                    pfrom->PushMessage(NetMsgType::GETDATA, vGetData);
                }
            }
        }
        CheckBlockIndex(chainparams.GetConsensus());
        }
        NotifyHeaderTip();
    }
    else if (strCommand == NetMsgType::BLOCK && !fImporting && !fReindex) 
    {
        CBlock block;
        vRecv >> block;
        LogPrint("net", "received block %s peer=%d\n", block.GetHash().ToString(), pfrom->id);
        CValidationState state;
        
        
        
        
        bool forceProcessing = pfrom->fWhitelisted && !IsInitialBlockDownload();
        ProcessNewBlock(state, chainparams, pfrom, &block, forceProcessing, NULL);
        int nDoS;
        if (state.IsInvalid(nDoS)) {
            assert (state.GetRejectCode() < REJECT_INTERNAL); 
            pfrom->PushMessage(NetMsgType::REJECT, strCommand, (unsigned char)state.GetRejectCode(),
                               state.GetRejectReason().substr(0, MAX_REJECT_MESSAGE_LENGTH), block.GetHash());