rocketpool-cli gives unhelpful error message when rocketpool-api isn't running

[jshufro]

Add a flag to v2 command definitions that informs the binary whether or not those commands rely on rocketpool_node.

For commands that do, check the docker daemon to see if rocketpool_node is running before attempting to run those commands.

Right now, should rocketpool_api/rocketpool_node not be running, those commands reply with:
Could not do x: exit status 1 which is distinctly unhelpful