Update operations must be PATCH and not PUT

[gtema]

python keystone implements user update as a PATCH (https://docs.openstack.org/api-ref/identity/v3/index.html#update-user) operation and not PUT how this project implements. It must be changed to PATCH for consistency. The same is actually applicable to every other operation.

[gtema]

for v3 we should only expose update operations as PATCH, for v4 we should expose update handler as PATCH and PUT.