Implements test_update_all_metadata_field_error.

Replace all metadata for a server with blank key metadata
forcing a error.

Blueprint missing-tempest-tests

Change-Id: I76fb4d019d2ff5eda50a8e3ee5797bebc7c25b84
diff --git a/tempest/tests/compute/servers/test_server_metadata.py b/tempest/tests/compute/servers/test_server_metadata.py
index 7896466..cdfe2f1 100644
--- a/tempest/tests/compute/servers/test_server_metadata.py
+++ b/tempest/tests/compute/servers/test_server_metadata.py
@@ -233,3 +233,12 @@
         self.assertRaises(exceptions.OverLimit,
                           self.client.update_server_metadata,
                           self.server_id, req_metadata)
+
+    @attr(type='negative')
+    def test_update_all_metadata_field_error(self):
+        # Raise a bad request error for blank key.
+        # set_server_metadata will replace all metadata with new value
+        meta = {'': 'data1'}
+        self.assertRaises(exceptions.BadRequest,
+                          self.client.set_server_metadata,
+                          self.server_id, meta=meta)