Make docker.sock hunting optional

[berney]

The docker.sock hunting often hangs or takes a very long time depending on the runtime and what sockets are in the container/host.

This PR makes it optional, default off (this is a behaviour change). I tried to make default true but then I could find how to have the CLI flag turn it off, I don't understand pkg/cli properly, or perhaps its not possible.

After this PR:

• Run amicontained -s to look for docker.sock (the old behaviour).
• Run amicontained to skip looking for docker.sock