The apitest.linux package is for running random bash commands,
running 'bitcoind -regtest', running random 'bitcoin-cli -regtest'
commands, and spinning up Bisq apps such as seednode, arbnode,
and bob & alice nodes.
All but random bash and bitcoin-cli commands are run in the background.
The bitcoin-cli response processing is crude; a more sophiticated
bitcoin-core rpc interface is not in the scope of this PR.
ApiTestConfig works like :common Config, but specific to this subproject.
BisqAppConfig is an enumeration specifying Bisq desktop and daemon
options for running seednode, arbnode, bob & alices nodes in regtest /
full-dao mode.