Convert oslo.service to using stestr

With the upgrade to oslotest 3.6.0 [0], testr no longer works [1].
This is because oslotest no longer requires testr and we don't depend
on it directly in oslo.service. Let's switch to using stestr, too!
Everyone's doing it...
This patch follows [2] in oslo.policy

[0] openstack/requirements@d5a3c58
[1] openstack/oslotest@897823f
[2] https://review.openstack.org/#/c/579295/

Change-Id: Ia82a17fe26b41730c8c323819591523d66a8cb36

.gitignore

@@ -25,8 +25,7 @@ pip-log.txt
 .coverage
 cover
 .tox
-nosetests.xml
-.testrepository
+.stestr
 
 # Translations
 *.mo

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./oslo_service/tests
+top_path=./

lower-constraints.txt

@@ -65,8 +65,8 @@ smmap==0.9.0
 snowballstemmer==1.2.1
 Sphinx==1.6.2
 sphinxcontrib-websupport==1.0.1
+stestr==2.0.0
 stevedore==1.20.0
-testrepository==0.0.18
 testtools==2.2.0
 traceback2==1.4.0
 unittest2==1.1.0

test-requirements.txt

@@ -6,7 +6,8 @@ fixtures>=3.0.0 # Apache-2.0/BSD
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
-requests
+requests>=2.14.2 # Apache-2.0
+stestr>=2.0.0 # Apache-2.0
 
 # These are needed for docs generation/testing
 openstackdocstheme>=1.18.1 # Apache-2.0

tox.ini

@@ -15,7 +15,7 @@ deps =
 whitelist_externals = find
 commands =
     find . -type f -name "*.py[co]" -delete
-    python setup.py testr --slowest --testr-args='{posargs}'
+    stestr run --slowest {posargs}
 
 [testenv:pep8]
 basepython = python3