Make compute keypairs_client use rest_client

Now service_client is unnecessary because that is the same as
rest_client. This patch makes keypairs_client use the rest_client,
and we will remove service_client for the cleanup in the future.

Partially implements blueprint consistent-service-method-names

Change-Id: I250c7a4de9585dd299cddd515e141635095d1a5a
1 file changed