Move unit tests execution to stestr

From time to time, unit tests execution fails with error:
"TypeError: 'NoneType' object is not iterable". It seems that
problem is in unittest2 library, which is used by testtools for
executing the tests.
Stestr lib is usinig unittest by default and the problem does not appear
for several hundred launches.

Change-Id: Ic1053353a87ebd44f20c607651772928020b9e66
Closes-Bug: #1874535

.gitignore

@@ -29,6 +29,7 @@ cover/
 nosetests.xml
 .testrepository
 .venv
+.stestr/
 
 # Translations
 *.mo

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./validations_common/tests
+top_dir=./

.testr.conf

@@ -1,7 +0,0 @@
-[DEFAULT]
-test_command=OS_STDOUT_CAPTURE=${OS_STDOUT_CAPTURE:-1} \
-             OS_STDERR_CAPTURE=${OS_STDERR_CAPTURE:-1} \
-             OS_TEST_TIMEOUT=${OS_TEST_TIMEOUT:-60} \
-             ${PYTHON:-python} -m subunit.run discover -t ./ . $LISTOPT $IDOPTION
-test_id_option=--load-list $IDFILE
-test_list_option=--list

lower-constraints.txt

@@ -104,6 +104,7 @@ smmap2==2.0.3
 snowballstemmer==1.2.1
 Sphinx==1.8.0
 sphinxcontrib-websupport==1.0.1
+stestr==3.0.1
 stevedore==1.28.0
 tenacity==5.0.1
 testrepository==0.0.18

test-requirements.txt

@@ -7,7 +7,7 @@ hacking>=3.0,<3.1.0 # Apache-2.0
 
 coverage!=4.4,>=4.0 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0
-testrepository>=0.0.18 # Apache-2.0/BSD
+stestr>=3.0.1 # Apache-2.0
 testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT
 reno>=2.5.0 # Apache-2.0

tox.ini

@@ -19,7 +19,9 @@ setenv =
   # paramiko CryptographyDeprecationWarning: https://github.com/ansible/ansible/issues/52598
   PYTHONWARNINGS=ignore:DEPRECATION::pip._internal.cli.base_command,ignore::UserWarning
   PIP_DISABLE_PIP_VERSION_CHECK=1
-commands = python setup.py test --slowest --testr-args='{posargs}'
+commands =
+  stestr run {posargs}
+  stestr slowest
 sitepackages = True
 deps =
     -c {env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}