[Python] Add support for request timeout

[mbohlool]

PR checklist

• Read the contribution guildelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates)
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

Similar to #4166 adding support for a timeout flag called _request_timeout.

fixes #4169

[wing328]

Travis CI failed with the following error:

======================================================================
ERROR: test_timeout (tests.test_pet_api.PetApiTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/tests/test_pet_api.py", line 117, in test_timeout
    self.pet_api.add_pet(body=self.pet, _request_timeout=5)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/apis/pet_api.py", line 78, in add_pet
    (data) = self.add_pet_with_http_info(body, **kwargs)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/apis/pet_api.py", line 164, in add_pet_with_http_info
    collection_formats=collection_formats)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/api_client.py", line 326, in call_api
    _return_http_data_only, collection_formats, _preload_content, _Using 3801113795 as seed
request_timeout)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/api_client.py", line 150, in __call_api
    _request_timeout=_request_timeout)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/api_client.py", line 371, in request
    body=body)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/rest.py", line 257, in POST
    body=body)
  File "/home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/python/petstore_api/rest.py", line 136, in request
    if isinstance(_request_timeout, (int, long)):
NameError: name 'long' is not defined

Ref: https://api.travis-ci.org/jobs/175005279/log.txt?deansi=true

Please take a look when you've time.

[mbohlool]

I've updated the test and it should pass now.

[wenbochang]

@mbohlool @wing328 thank you for this feature! is there a way to configure this timeout when generating the client?

We generate like this:

        'docker run -v {output}:/local -v {spec_path}:/spec.yml '
        'swaggerapi/swagger-codegen-cli:v2.3.1 generate -i '
        '/spec.yml -l {language} -o /local '
        '-DpackageName={package_name}')

But it seems the client side just uses urllib3's urlopen and the default timeout for that is infinite