Improving the code quality of utilities by adding the flake8 check on
zuul and adding the flake8-import-order plugin to standardize imports.
Also, defaults testenv to python3.9 configuration that should be used
for now on with the debian migration.
Story: 2010100
Task: 45671
Signed-off-by: Thiago Brito <thiago.brito@windriver.com>
Change-Id: I007302bdfb873aed4ebb7b9023db2461282b9fba
c213a3832d