Catch new urllib3 exception: ProtocolError

The new version of requests (2.4.0) has updated underlying urllib3
to version 1.9. Unfortunately urllib3 introduced new exception
ProtocolError. Because of that unit tests in glance are failing:
ProtocolError: ('Connection aborted.', gaierror(-2, 'Name or service not known'))

To solve this problem new urllib3 exception is caught in the same place
that the old one was. Unfortunately both exception are still in use so
I couldn't remove the old one.

Change-Id: I55eef98e734c59b9b627f182768a633b2b701e43
Closes-Bug: #1364893
Support for Metadata Definitions Catalog API

API calls and shell commands added in this patch:
- CRUD for metadefs namespaces;
- CRUD for metadefs objects;
- CRUD for metadefs properites;
- CRD for metadefs resource types and resource type associations.

Change-Id: I6d15f749038e8fd24fc651f0b314df5be7c673ef
Implements: blueprint metadata-schema-catalog-support
Co-Authored-By: Facundo Maldonado <facundo.n.maldonado@intel.com>
Co-Authored-By: Michal Dulko <michal.dulko@intel.com>
Co-Authored-By: Lakshmi N Sampath <lakshmi.sampath@hp.com>
Co-Authored-By: Pawel Koniszewski <pawel.koniszewski@intel.com>