Add a function `WaitBlocks` to wait for blocks to propagate to all three
nodes, and use this instead of waiting a fixed time of one second.
Fixes#3445.
qa/rpc-tests/wallet.sh runs a three-node -regtest network,
generates a fresh blockchain, and then exercises basic wallet
sending/receiving functionality using command-line RPC.
* Use the latest version, with limited memory usage, and path to
on-disk db (try mouting qa/tmp on a tmpfs)\
* enable -debug=net
* re-enable BitcoindComparisonTool in pull-tester
Re-organize the pull-tester scripts a bit.
And disables running the blockchain tester, it is not working properly
on the pull-tester machine for reasons I cannot explain (fails to start).
