Ensure Docker client uses exit codes when errors occur

This patchset essentially ensures that the Docker client actually exits with error codes if an error is encountered.

Docker-DCO-1.1-Signed-off-by: Aleksa Sarai <cyphar@cyphar.com> (github: cyphar)
But I told you reason about GC :) Maybe this is not very big problem for client-side, but this is bad `go`-code and I just want you to know this. This can help you in your future contributions, when you will choose your own interface.