Display all clusters in Compute Rate Assignment page

fixing https://bugzilla.redhat.com/show_bug.cgi?id=1456825

Fix displaying clusters in Compute Rate Assignment page when
selecting 'Selected Cluster/Deployment Roles' in Assign to drop
down menu even when clusters have the same name (and belong to
different providers) so the name of their providers was added
to their original names as prefix.

app/controllers/chargeback_controller.rb

@@ -786,6 +786,10 @@ def get_cis_all
     @edit[:cb_assign][:hierarchy] ||= {}
     all_of_classtype.each do |instance|
       @edit[:cb_assign][:cis][instance.id] = instance.name
+      if klass == "ems_cluster"
+        provider_name = instance.ext_management_system.name
+        @edit[:cb_assign][:cis][instance.id] = provider_name + "/" + instance.name
+      end
       next unless klass == "tenant" && instance.root?
       @edit[:cb_assign][:hierarchy][instance.id] = {}
       @edit[:cb_assign][:hierarchy][instance.id][:name] = instance.name