Fix identity tests when domain specific drivers are enabled

This updates users and groups identity tests to check the existence
of domain specific drivers and, therefore, the existence of users
and groups on different domain drivers.

This adds a new feature flag to be used when domain specific drivers
are enabled.

Change-Id: Iedb470c51fa2174ab7651e6b7e22eff1f25f7aac
diff --git a/releasenotes/notes/identity-tests-domain-drivers-76235f6672221e45.yaml b/releasenotes/notes/identity-tests-domain-drivers-76235f6672221e45.yaml
new file mode 100644
index 0000000..7ed3081
--- /dev/null
+++ b/releasenotes/notes/identity-tests-domain-drivers-76235f6672221e45.yaml
@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    A new boolean config option ``domain_specific_drivers``
+    is added to the section ``identity-feature-enabled``.
+    This option must be enabled when testing an environment that
+    is configured to use domain-specific identity drivers.