[python][fastapi] various minor improvements (#9672)

* fix python fastapi tests, update readme, add CI test

* update FILES

* use virtualenv

* fix pom.xml

* skip flake8

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

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+set -e
+
+REQUIREMENTS_FILE=requirements.txt
+REQUIREMENTS_OUT=requirements.txt.log
+SETUP_OUT=*.egg-info
+VENV=.venv
+DEACTIVE=false
+
+export LC_ALL=en_US.UTF-8
+export LANG=en_US.UTF-8
+
+### set virtualenv
+if [ -z "$VIRTUAL_ENV" ]; then
+		virtualenv $VENV --no-site-packages --always-copy --python python3
+		source $VENV/bin/activate
+    DEACTIVE=true
+fi
+
+### install dependencies
+pip install -r $REQUIREMENTS_FILE | tee -a $REQUIREMENTS_OUT
+
+### run tests
+PYTHONPATH=src pytest tests
+
+### static analysis of code
+#flake8 --show-source src/
+
+### deactivate virtualenv
+if [ $DEACTIVE == true ]; then
+    deactivate
+fi