Removes Windows dependencies in metadata services

Removes dependencies from utils.windows.x509 in the metadata
services.

cloudbaseinit/utils/x509constants.py

@@ -0,0 +1,16 @@
+# Copyright 2014 Cloudbase Solutions Srl
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+PEM_HEADER = "-----BEGIN CERTIFICATE-----"
+PEM_FOOTER = "-----END CERTIFICATE-----"