fix: docker check on osx incorrectly failing

[colesnodgrass]

• on osx, don't fail the docker check if the second attempt is successful
  • On osx, docker can be communicated with via /var/run/docker.sock or ~/.docker/run/docker.sock. The existing code was incorrectly failing this check if the second attempt (~/.docker/run/docker.sock) was successful.
• fix typo in error messages - coud -> could
• add context to docker.New call
• call Ping on the docker client before marking the client creation as successful
  • Fix an issue where the client would be created but would fail when communicating with it at a later step. This early Ping check establishes that we can communicate with the docker daemon before we consider our client successfully created.