Add command for listing all available steps

[thozza]

Add command that would list all available Steps based on the tests.conf and local steps. This would help the test developer to now what Steps are already implemented and can be reused. The option could be something like # ctf-cli list-steps. Output could contain the name of the remote tests repository and the list of Steps available in it.

[vrutkovs]

We probably should parse the output of behave -f steps -d

[thozza]

I'm for anything that will do the job. The command you've noted will fail if there is something messed up in environment.py or if something can not be imported. Another approach would be just go through all the steps/*.py files. But letting behave handle this seems like a good approach.

[vrutkovs]

Additional feature: list params, accepted by environment.py, currently Dockerfile or Image