Update regions tests to work w/ pre-prov

I don't see any limitations by using pre-provisioned
credentials for this test:

* test_list_regions_filter_by_parent_region_id
* test_create_region_with_specific_id
* test_create_update_get_delete_region
* test_list_regions

By setting force_tenant_isolation=False this test can now
be executed with backends that don't allow user creation
(immutable user source) like LDAP.

Change-Id: Ifad293dddb7c7fe76005761b43e1252e40ce7bdc
diff --git a/tempest/api/identity/admin/v3/test_regions.py b/tempest/api/identity/admin/v3/test_regions.py
index f22a528..c8c0151 100644
--- a/tempest/api/identity/admin/v3/test_regions.py
+++ b/tempest/api/identity/admin/v3/test_regions.py
@@ -20,6 +20,10 @@
 
 
 class RegionsTestJSON(base.BaseIdentityV3AdminTest):
+    # NOTE: force_tenant_isolation is true in the base class by default but
+    # overridden to false here to allow test execution for clouds using the
+    # pre-provisioned credentials provider.
+    force_tenant_isolation = False
 
     @classmethod
     def setup_clients(cls):