Add stestr master job

Tempest use stestr to run the tests, adding
a experimental and periodic job to run Tempest
with stestr master will help to detect any
breaking change in advance.

Change-Id: Ice57e193c5150be7141e0e003be5091a191b854c
diff --git a/tox.ini b/tox.ini
index 2315163..cd32174 100644
--- a/tox.ini
+++ b/tox.ini
@@ -409,3 +409,15 @@
 allowlist_externals = bash
 commands =
   bash tools/tempest-plugin-sanity.sh
+
+[testenv:stestr-master]
+envdir = .tox/tempest
+sitepackages = {[tempestenv]sitepackages}
+basepython = {[tempestenv]basepython}
+setenv = {[tempestenv]setenv}
+deps = {[tempestenv]deps}
+# The below command install stestr master version and run smoke tests
+commands =
+    find . -type f -name "*.pyc" -delete
+    pip install -U git+https://github.com/mtreinish/stestr
+    tempest run --regex '\[.*\bsmoke\b.*\]' {posargs}