[FT] Run all .*MySQL tests in an isolated thread

This change in the "dsvm-functional" job definition will avoid the
parallel execution of any MySQL test.

Related-Bug: #1962594
Change-Id: I4fe6a6920b9b2711563e85b51f18a9d5a9086ceb
(cherry picked from commit 7d5ee70)

Author: ralonsoh

tox.ini

@@ -63,7 +63,8 @@ deps =
   {[testenv:functional]deps}
 commands =
   {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
-  stestr run --group_regex=(.*MySQL\.|.*PostgreSQL\.) {posargs}
+  stestr run --group-regex .*PostgreSQL\. --exclude-regex .*MySQL\. {posargs}
+  stestr run --combine --concurrency 1 .*MySQL\. {posargs}
 
 [testenv:dsvm-fullstack]
 setenv = {[testenv]setenv}