Flipper test in qa/rpc-tests/wallet.sh

[laanwj]

(from discussion in #3346)
Heavy system load can cause an error in the wallet test.

+ /mnt/bitcoin/qa/rpc-tests/wallet.sh /mnt/bitcoin/linux-build/src
bad balance: 21.00000000 (expected 100)

Probably it happens here:
https://github.com/bitcoin/bitcoin/blob/master/qa/rpc-tests/wallet.sh#L84

The test does a fixed wait for 1 second to give the block time to relay, but this may not always be enough in the case of heavy load.

Simple (but unreliable and slow) solution would be to increase the timeout, a more thorough solution would be to provide a way to wait for block propagation.

[laanwj]

I managed to reproduce this problem locally. The problem is indeed in propagation:

B1: 204 blocks
B2: 204 blocks
B3: 203 blocks

I'm going to add a function WaitBlocks that waits until all three nodes have the same amount of blocks, and replace that for the sleep 1s.

[sipa]

ACK