Add negative test: create domain with empty name

Add negative test 'create domain with empty name' to
test_domains_negative

Change-Id: Ia3acbc3e1334cf39de5db3c96487e32cff5f088e
Partial-Bug: 1513346
diff --git a/tempest/api/identity/admin/v3/test_domains_negative.py b/tempest/api/identity/admin/v3/test_domains_negative.py
index 156179c..33819a8 100644
--- a/tempest/api/identity/admin/v3/test_domains_negative.py
+++ b/tempest/api/identity/admin/v3/test_domains_negative.py
@@ -37,3 +37,10 @@
         # domain need to be disabled before deleting
         self.assertRaises(lib_exc.Forbidden, self.client.delete_domain,
                           domain_id)
+
+    @test.attr(type=['negative'])
+    @test.idempotent_id('9018461d-7d24-408d-b3fe-ae37e8cd5c9e')
+    def test_create_domain_with_empty_name(self):
+        # Domain name should not be empty
+        self.assertRaises(lib_exc.BadRequest, self.client.create_domain,
+                          name='')