Integration CLI tests

[AshwinHIBM]

Scripts to run tests in https://github.com/docker/cli.
The job triggering this script: ppc64le-cloud/test-infra#483

[ppc64le-cloud-bot]

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[clnperez]

LGTM
Would like to know if there's a better way to check for failure than grepping, but if not we can merge

[AshwinHIBM]

The exit code is non-zero irrespective of failure/success, hence grep looks like the only reliable option at the moment. Let's see if we find a better way to get the correct exit code in a follow-up PR.