Create docker client from environment variables

[rathko]

Why:

Currently kompose works only with the hard-coded Unix socket endpoint, which makes it difficult to use with macOS and other non-Linux environments.

What:

Detect if the DOCKER_HOST is set and create a docker client from the environment variables DOCKER_HOST, DOCKER_TLS_VERIFY, and DOCKER_CERT_PATH.

[kompose-bot]

@rathko, thank you for the pull request! We'll ping some people to review your PR. @cdrage and @surajnarwade, please review this.

[k8s-ci-robot]

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[cdrage]

Hey @rathko

Thanks for the contribution!

A few things:

• Gotta sign the CLA (pain in the ass I know)

• Do you mind re-basing? I just enabled cluster building for Kubernetes hence the reason why SemaphoreCI just failed

• Tests fail, mind doing a gofmt on the code? Gotta fix some of that indentation.

[rathko]

@cdrage Thanks, it's rebased, gofmted and CLA is signed. Cheers

[cdrage]

SemaphoreCI is being funky, but tests pass and code LGTM 👍

[surajnarwade]

@rathko , Thanks for contribution :)
LGTM for code 👍

[cdrage]

LGTM thanks for the contribution @rathko !