Switch to using stestr

According to Openstack summit session [1] stestr is maintained
project to which all Openstack projects should migrate.
Let's switch it then.

[1] https://etherpad.openstack.org/p/YVR-python-pti

Also fix the lower-requiremenst.txt to pass the gate.

Change-Id: I498282defd87c4ea16979b729600a179cdd3d01f
Signed-off-by: Charles Short <zulcss@gmail.com>

lower-constraints.txt

@@ -1,8 +1,10 @@
 appdirs==1.3.0
 Babel==2.3.4
 bandit==1.4.0
+cassandra-driver===2.1.4
 coverage==4.0
 debtcollector==1.2.0
+elasticsearch===2.0.0
 extras==1.0.0
 fixtures==3.0.0
 flake8==2.5.5
@@ -12,6 +14,7 @@ gitdb==0.6.4
 GitPython==1.0.1
 greenlet==0.4.10
 hacking==0.12.0
+influxdb===2.9.2
 iso8601==0.1.11
 kazoo==2.2
 keystoneauth1==3.4.0

test-requirements.txt

@@ -7,4 +7,4 @@ hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
 coverage!=4.4,>=4.0 # Apache-2.0
 mock>=2.0.0 # BSD
 oslotest>=3.2.0 # Apache-2.0
-os-testr>=1.0.0 # Apache-2.0
+stestr>=1.0.0 # Apache-2.0

tox.ini

@@ -26,7 +26,7 @@ deps =
 commands =
   find {toxinidir} -type f -name "*.py[c|o]" -delete
   rm -Rf .testrepository/times.dbm
-  ostestr {posargs}
+  stestr run {posargs}
 
 [testenv:cover]
 setenv =