[WIP] Validate if Runner process exists

[davidjurado]

When executing MLCube whiout Docker installed or running there is a long error message indicating that it's possible that Docker isn't running (Is the docker daemon running?) but this message is at the top of other outputs and it's hard to understand the actual error, the idea of this PR is to provide a better error message by checking if there aren't any Docker processes running and provide a simpler output.

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[dfeddema]

We need to verify that either docker or podman are available. Both docker and podman use the docker runner, hence for the podman user docker will likely not be running and will not need to be for mlcube to work correctly using the docker runner. The podman user specifies "alias docker=podman" and uses the docker_runner. Installation instructions for podman on mac, windows, linux are here: https://podman.io/getting-started/installation