Use Sequel's any_not_empty extension

There are already several PRs (see below [1]) that change dataset.any?
to !dataset.empty? or otherwise mention the difference between these two
statements. Whereas the first one fetches all data from the database to
then check if the resulting array contains at least one element, the
second statement does a 'select 1 as one from table limit 1' query that
has a far better performance.

Fortunately there is a Sequel extension (see [2]) that 'fixes' this
misleading behavior; so instead of searching for more places where we
could change the implementation, using dataset.any? should now be
equivalent to !dataset.empty? and everyone can choose freely which one
to use.

[1]
cloudfoundry#2117
cloudfoundry#2533
cloudfoundry#2803
cloudfoundry#2855

[2] https://sequel.jeremyevans.net/rdoc-plugins/files/lib/sequel/extensions/any_not_empty_rb.html

app/models/services/service_broker.rb

@@ -47,11 +47,11 @@ def space_scoped?
     end
 
     def has_service_instances?
-      !VCAP::CloudController::ServiceInstance.
+      VCAP::CloudController::ServiceInstance.
         join(:service_plans, id: :service_plan_id).
         join(:services, id: :service_id).
         where(services__service_broker_id: id).
-        empty?
+        any?
     end
 
     def self.user_visibility_filter(user)

lib/cloud_controller/db.rb

@@ -94,6 +94,7 @@ def self.load_models_without_migrations_check(db_config, logger)
 Sequel::Model.plugin :validation_helpers
 
 Sequel::Database.extension(:current_datetime_timestamp)
+Sequel::Database.extension(:any_not_empty)
 
 require 'cloud_controller/encryptor'
 Sequel::Model.include VCAP::CloudController::Encryptor::FieldEncryptor

spec/unit/models/services/service_broker_spec.rb

@@ -213,7 +213,7 @@ module VCAP::CloudController
         end
 
         it 'does a single db query' do
-          expect { service_broker.has_service_instances? }.to have_queried_db_times(/select/i, 1)
+          expect { service_broker.has_service_instances? }.to have_queried_db_times(/select 1.*limit 1/i, 1)
         end
       end
 
@@ -223,7 +223,7 @@ module VCAP::CloudController
         end
 
         it 'does a single db query' do
-          expect { service_broker.has_service_instances? }.to have_queried_db_times(/select/i, 1)
+          expect { service_broker.has_service_instances? }.to have_queried_db_times(/select 1.*limit 1/i, 1)
         end
       end
     end