QA: add --noshutdown option to prevent stopping nodes
QA: add --noshutdown option to prevent stopping nodes

With `--noshutdown`, the nodes are not stopped explicitly. `--noshutdown` implies `--nocleanup`, to prevent removing datadirs, which are still in use.

wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin,wastholm/bitcoin