[AIRFLOW-4833] Allow to set Jinja env options in DAG declaration

[galak75]

Make sure you have checked all steps below.

Jira

• [ x ] 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-4833
  • In case you are fixing a typo in the documentation you can prepend your commit with [AIRFLOW-XXX], code changes always need a Jira issue.
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Description

• [ x ]
• Issue was : a trailing newline in a template string is dropped by Jinja2 (default behavior)
• This is fixed by allowing to set options to jinja2.Environment object by defining these options at the DAG level (see AIRFLOW-4833 for more information)

Tests

• [ x ] My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

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  4. Subject uses the imperative mood ("add", not "adding")
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  6. Body explains "what" and "why", not "how"

Documentation

• [ x ] In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain docstrings that explain what it does
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Code Quality

• [ x ] Passes flake8

[galak75]

@kaxil @BasPH : This PR relates to this thread on slack. Maybe you can review it? ;-)

[kaxil]

Can we add this parameter in docstring of DAG class please?

[kaxil]

LGTM. Can you please add the parameter in docstring and also copy the example you have in docs/concepts.rst in the docstring

[galak75]

LGTM. Can you please add the parameter in docstring and also copy the example you have in docs/concepts.rst in the docstring

Sure! My bad... I forgot it.
It's done, build is in queue in Travis