Use openstack-images-v2.1-json-patch for update method

image.patch returns a JSON schema Draft 10 (application/openstack-images-v2.1-json-patch)
while the glaceclient update method specify a Content-Type header
application/openstack-images-v2.0-json-patch with correspond to a JSON schemea Draft 4.

Fixes bug 1206095
Change-Id: I8c5a96f0e117a81b5b527a96ef45758fc69b518d
Merge "Use openstack-images-v2.1-json-patch for update method"