Add dsvm-functional-gate tox environment

In the neutron gate we want to run functional tests in 2 steps:
* all tests except MySQL and PostgreSQL tests,
* MySQL and PostgreSQL tests runs serially

And that was done like that in the dsvm-functional tox environment.
But there is no really point to run it as such always when someone
e.g. runs some tests from the functional tests suite locally, using
dsvm-functional environment.
So this patch adds dsvm-functional-gate environment which will be used
in the Zuul jobs and will have this 2 steps configuration.
Regular dsvm-functional env will run all tests together.

Change-Id: Ic66d9961393d9dff64ebd14802ad38c18808b1da

tox.ini

@@ -62,6 +62,13 @@ setenv = {[testenv:functional]setenv}
          {[testenv:dsvm]setenv}
 deps =
   {[testenv:functional]deps}
+commands =
+  {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
+  stestr run {posargs}
+
+[testenv:dsvm-functional-gate]
+setenv = {[testenv:dsvm-functional]setenv}
+deps = {[testenv:dsvm-functional]deps}
 commands =
   {toxinidir}/tools/deploy_rootwrap.sh {toxinidir} {envdir}/etc {envdir}/bin
   stestr run --exclude-regex (.*MySQL\.|.*PostgreSQL\.) {posargs}

zuul.d/base.yaml

@@ -47,7 +47,7 @@
       devstack_localrc:
         INSTALL_TESTONLY_PACKAGES: true
         DATABASE_PASSWORD: stackdb
-      tox_envlist: dsvm-functional
+      tox_envlist: dsvm-functional-gate
       tox_constraints_file: '{{ ansible_user_dir }}/src/opendev.org/openstack/requirements/upper-constraints.txt'
       zuul_copy_output:
         # We need to copy directory with logs to have it in job artifacts also,