[Python] Updates python test framework to pytest (#4765)

* Switches python generators to use pytest, useNose CLI option added if to allow nose to be used instead

* Adds ensure-up-to-date changes

* Adds setup.cfg to python clients so we can configure nose when useNose=true

* Adds fix for python-aiohttp testing, adds files missing from ensure-up-to-date

samples/server/petstore/python-aiohttp/test_python3.sh

@@ -1,8 +1,7 @@
 #!/bin/bash
 
-REQUIREMENTS_FILE=requirements.txt
-TEST_REQUIREMENTS_FILE=test-requirements.txt
-REQUIREMENTS_OUT=requirements.txt.log
+REQUIREMENTS_FILE=dev-requirements.txt
+REQUIREMENTS_OUT=dev-requirements.txt.log
 SETUP_OUT=*.egg-info
 VENV=.venv
 DEACTIVE=false
@@ -12,16 +11,16 @@ export LANG=en_US.UTF-8
 
 ### set virtualenv
 if [ -z "$VIRTUAL_ENV" ]; then
-	virtualenv $VENV --no-site-packages --always-copy --python python3
+		virtualenv $VENV --no-site-packages --always-copy --python python3
 		source $VENV/bin/activate
     DEACTIVE=true
 fi
 
 ### install dependencies
-pip install -r $REQUIREMENTS_FILE -r $TEST_REQUIREMENTS_FILE | tee -a $REQUIREMENTS_OUT
+pip install -r $REQUIREMENTS_FILE | tee -a $REQUIREMENTS_OUT
 
 ### run tests
-pytest || exit 1
+tox || exit 1
 
 ### static analysis of code
 flake8 --show-source petstore_api/