docker: use official client instead of fsouza/go-dockerclient

[pkazmierczak]

This PR replaces fsouza/go-dockerclient 3rd party docker client library with
docker's official SDK.

Notes to reviewers:

• this PR is split into 3 commits, one containing driver logic, one for the
  unit tests, and one for go mod/sum
• the vast majority of the refactoring is pretty straightforward, replacing
  methods, changing argument orders and types. There are a few exceptions that
  require attention, namely:
  • any methods that utilize capturing stdio/stdout/stderr had to be re-written,
    e.g., dockerLogger.Start, driver.ExecTaskStreaming
  • signal handling in the task handler,
  • stats collector

[ahjohannessen]

@tgross Seems like this has a breaking change with regards to:

plugin "docker" {
    config {
        auth {
            config = "/etc/nomad.d/.docker-creds"

        }
    }
}

Nomad 1.8.4 the above works, bumping to 1.9.0 results in:

Failed to pull `quay.io/our-repo/app:0.0.1`: Error response from daemon: unauthorized: access to the requested resource is not authorized

[tgross]

@ahjohannessen please open a new issue