Optimise and fix queries, fix test description

Author: jochenehret

app/models/runtime/space.rb

@@ -269,12 +269,8 @@ def find_visible_service_instance_by_name(name)
       (shared | source).first
     end
 
-    def number_service_instances
-      service_instances_dataset.count
-    end
-
     def number_service_keys
-      ServiceKey.where(service_instance_id: service_instances_dataset.select(:id)).count
+      ServiceKey.join(:service_instances, id: :service_instance_id).where(service_instances__space_id: id).count
     end
 
     def self.user_visibility_filter(user)

app/presenters/v3/space_usage_summary_presenter.rb

@@ -8,7 +8,7 @@ def to_hash
           started_instances: started_instances,
           memory_in_mb: space.memory_used,
           routes: space.routes_dataset.count,
-          service_instances: space.number_service_instances,
+          service_instances: space.service_instances_dataset.count,
           reserved_ports: VCAP::CloudController::SpaceReservedRoutePorts.new(space).count,
           domains: space.organization.owned_private_domains_dataset.count,
           per_app_tasks: space.running_and_pending_tasks_count,

spec/unit/controllers/v3/spaces_controller_spec.rb

@@ -962,7 +962,7 @@
     context 'when the user has permissions to read from the space' do
       before { allow_user_read_access_for(user, orgs: [org], spaces: [space]) }
 
-      it 'throws ResourceNotFound error' do
+      it 'succeeds' do
         get :show_usage_summary, params: { guid: space.guid }
 
         expect(response).to have_http_status(:ok)