Eliminate jinja2 template expression warning and rename coreos-python var (#1911)

* Change deprecated vagrant ansible flag 'sudo' to 'become'

* Emphasize, that the name of the pip_pyton_modules is only considered in coreos

* Remove useless unused variable

* Fix warning when jinja2 template-delimiters used in when statement

There is no need for jinja2 template-delimiters like {{ }} or {% %}
any more. They can just be omitted as described in https://github.com/ansible/ansible/issues/22397

* Fix broken link in getting-started guide