Fix shell out to docker-classic when invoking

[gtardif]

What I did

• Changed shellout invocation from docker context inspect default to docker-classic context inspect default when getting default context to populate context ls
• Changed e2e tests to run with both docker and docker-classic in the path (more real user
  setup). This was causing docker context inspect default to fail and display docker help.

(not mandatory) A picture of a cute animal, if possible in relation with what you did

[gtardif]

Discussed with @rumpl, I had to move some unit tests into e2e tests, as they were relying on docker being in the path and actually being the "classic" docker version, in order to docker context inspect default. (and were overlapping a bit with existing e2e, I moved the golden files into e2e)