[AIRFLOW-5204] Shellcheck + common licences + executable shebangs in shell files

[potiuk]

Make sure you have checked all steps below.

Jira

• My PR addresses the following Airflow Jira issues and references them in the PR title. For example, "[AIRFLOW-XXX] My Airflow PR"
  • https://issues.apache.org/jira/browse/AIRFLOW-5204

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Tests

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Code Quality

• Passes flake8

[potiuk]

Again - another set of checks. This time for shell files (shellcheck + shebangs/executable + licenses)

[potiuk]

This one is badly needed I think. Having linted/shellchecked bash scripts in Airflow would be great to have.

[milton0825]

Looks good apart from one small nit.

[potiuk]

Thanks! merged.