[python] Fixes a breakage while deserializing the read-only attributes

[vvb]

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#9409 added _new_from_openapi_data and updated the code to invoke this method at most places except one. This PR takes care of updating this as well.
Deserialization of read-only attributes breaks without this change.

@spacether @wing328

Added a test that validates the fix.

Here is a snapshot of the same test failing when run on master branch codebase,

Here is a snapshot of the test passing when run against this PR branch,

[wing328]

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

[wing328]

@vvb thanks for the PR. Can you please add a test using Mole in the test spec or add a new schema with readonly properties to cover the case?

    Mole:
      type: object
      required:
        - blind
        - smell
        - hearing
      properties:
        blind:
          type: boolean
          readOnly: true
        smell:
          type: string
          readOnly: false
        touch:
          type: boolean
          readOnly: true
        taste:
          type: string
          readOnly: false
        hearing:
          type: boolean
        seeingGhosts:
          type: boolean

[vvb]

@spacether @wing328 I have taken care of the comments. I have also added a test that checks for this issue and attached snapshots of it passing against this branch, and failing against master (which does not have the fix yet).

Please check and update if anything more is required here.

[spacether]

Thank you for your PR. This looks great! Can you make the suggested small tweaks to:

• make the if statements use the dict.get check of _spec_property_naming
• remove the exception handling when importing module sin your test
• update your test to also check that the dog data was turned into a Dog instance

[vvb]

@spacether took care of the comments. here are the test results post changes,

[spacether]

Thanks for making those updates. This looks good.

[spacether]

Ci error is csharp-netcore and is unrelated