Fix create/show/delete methods on subnetpools_client

The targets of create/show/delete methods of subnetpools_client are
singular, and the methods' names of the other clients are singular.
So this aptch fixes subnetpools_client methods' names.

Partially implements blueprint consistent-service-method-names

Change-Id: I405a896b4da0c5cb5bc87622d07498c06932f406
2 files changed