Do not generate bytecode in tests

This is a known best practise during development, to avoid leaving
stale bytecode after a file is deleted.

Change-Id: Ic24e1cdb6c007f64aed379dd8cdc0482da4f52a3
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

tox.ini

@@ -4,15 +4,15 @@ minversion = 4.28.0
 
 [testenv]
 usedevelop = True
+setenv =
+  PYTHONDONTWRITEBYTECODE=1
 constraints =
   {env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
 deps =
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
 commands =
-  find . -type f -name "*.py[c|o]" -delete
   stestr run --slowest {posargs}
-allowlist_externals = find
 
 [testenv:debug]
 commands = oslo_debug_helper -t heatclient/tests {posargs}
@@ -29,12 +29,14 @@ commands = {posargs}
 
 [testenv:functional]
 setenv =
+  {[testenv]setenv}
   OS_TEST_PATH = ./heatclient/tests/functional
   CLIENT_NAME=python-heatclient
 passenv = OS_*
 
 [testenv:cover]
 setenv =
+  {[testenv]setenv}
   PYTHON=coverage run --source heatclient --parallel-mode
 commands =
   stestr run {posargs}