[python] Skip adding None value in query parameters

[ghost]

If we send None for a non mandatory query parameter. OpenAPIGenerator now makes the URL something like ?query=None this should not be passed as the string None rather should be ignored as None is a special keyword

If the user passes the query as "None" (Str) only then url should be considered as ?query=None

fixes #4151

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[ghost]

@taxpon (2017/07) @frol (2017/07) @mbohlool (2017/07) @cbornet (2017/09) @kenjones-cisco (2017/11) @tomplus (2018/10) @Jyhess (2019/01)

cc: @wing328

[wing328]

LGMT. Let's wait for the CI test results.

[ghost]

👍

[wing328]

CI failure not related to this PR.