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

Change-Id: I93718ec3a72ac560aca4c9c84d1ac6078adbe090
Signed-off-by: Chuck Short <chucks@redhat.com>

lower-constraints.txt

@@ -60,7 +60,7 @@ openstackdocstheme==1.18.1
 openstacksdk==0.12.0
 os-client-config==1.28.0
 os-service-types==1.2.0
-os-testr==1.0.0
+stestr==1.0.0
 osc-lib==1.10.0
 oslo.concurrency==3.25.0
 oslo.config==5.2.0

test-requirements.txt

@@ -7,7 +7,7 @@ coverage!=4.4,>=4.0 # Apache-2.0
 ddt>=1.0.1 # MIT
 docker>=2.4.2 # Apache-2.0
 hacking!=0.13.0,<0.14,>=0.12.0 # Apache-2.0
-os-testr>=1.0.0 # Apache-2.0
+stestr>=1.0.0 # Apache-2.0
 oslo.serialization!=2.19.1,>=2.18.0 # Apache-2.0
 openstackdocstheme>=1.18.1 # Apache-2.0
 oslotest>=3.2.0 # Apache-2.0

tools/ostestr_compat_shim.sh

@@ -2,7 +2,7 @@
 
 # preserve old behavior of using an arg as a regex when '--' is not present
 case $@ in
-    (*--*) ostestr $@;;
-    ('') ostestr;;
-    (*) ostestr --regex "$@"
+    (*--*) stestr run $@;;
+    ('') stestr run;;
+    (*) stestr run --regex "$@"
 esac