Import LDAP job into project

Import the legacy-tempest-dsvm-ldap-domain-specific-driver job[1] into the
keystone repo and convert it to be Zuulv3 native.

This cherry-pick removes the explicit use of python3 since it doesn't
quite work on this old of a branch.

[1] https://opendev.org/openstack/openstack-zuul-jobs/src/branch/master/playbooks/legacy/tempest-dsvm-ldap-domain-specific-driver

Change-Id: Ie0b9f13d6fb06b776d6a58d5d1087c20df8a7cda
Needed-by: https://review.opendev.org/687444
(cherry picked from commit 52ab0cf579)
(cherry picked from commit 0f6c6061b3)
(cherry picked from commit 429923fbb3)
(cherry picked from commit 2f71550654)
(cherry picked from commit 8b8a8f2c54)

.zuul.yaml

@@ -1,3 +1,13 @@
+- job:
+    name: keystone-dsvm-ldap-domain-specific-driver
+    parent: devstack-tempest
+    vars:
+      devstack_localrc:
+        KEYSTONE_CLEAR_LDAP: 'yes'
+        LDAP_PASSWORD: 'nomoresecret'
+      devstack_services:
+        ldap: true
+
 - project:
     templates:
       - openstack-python-jobs
@@ -20,7 +30,7 @@
               - ^keystone/tests/unit/.*$
               - ^releasenotes/.*$
         - openstack-tox-cover
-        - legacy-tempest-dsvm-ldap-domain-specific-driver:
+        - keystone-dsvm-ldap-domain-specific-driver:
             voting: false
             irrelevant-files:
               - ^(test-|)requirements.txt$