Clean-up - Unnecessary trailing underscores in Python Flask, AIOHttp, BluePlanet (#16249)

* Remove trailing underscore in security_controller_.py and base_model_.py

* Regenerating sample files

* Clean-up files with trailing underscore in samples

* Update security extension to use the new security_controller

* Regenerate unmaintained samples

samples/openapi3/server/petstore/python-flask-python2/Dockerfile

@@ -1,16 +1,16 @@
-FROM python:2-alpine
+FROM python:3-alpine
 
 RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app
 
 COPY requirements.txt /usr/src/app/
 
-RUN pip install --no-cache-dir -r requirements.txt
+RUN pip3 install --no-cache-dir -r requirements.txt
 
 COPY . /usr/src/app
 
 EXPOSE 8080
 
-ENTRYPOINT ["python"]
+ENTRYPOINT ["python3"]
 
 CMD ["-m", "openapi_server"]