[webui] Clarify what set_bugowner does

Show in the request that the previous bigowners will be deleted.
This makes more clear the difference between `add_role` bugowner and
`set_bugowner`.

src/api/app/helpers/webui/webui_helper.rb

@@ -366,7 +366,7 @@ def requester_str(creator, requester_user, requester_group)
   end
 
   def creator_intentions(role = nil)
-    role.blank? ? 'become bugowner' : "get the role #{role}"
+    role.blank? ? 'become bugowner (previous bugowners will be deleted)' : "get the role #{role}"
   end
 
   # If there is any content add the ul tag

src/api/spec/helpers/webui/webui_helper_spec.rb

@@ -391,7 +391,7 @@
 
   describe '#creator_intentions' do
     it 'do not show the requester if he is the same as the creator' do
-      expect(creator_intentions(nil)).to eq 'become bugowner'
+      expect(creator_intentions(nil)).to eq 'become bugowner (previous bugowners will be deleted)'
     end
 
     it 'show the requester if he is different as the creator' do