Major Description
The fact that we currently don't support SET type in Attribute means that operators might end up having multiple attributes (e.g., slave attributes) with the same name and type but different value.
But the comparator operator for Attributes expects unique (name, type) Attributes. This results in slave recovery failure when comparing checkpointed attributes with those set via flags.
https://issues.apache.org/jira/browse/MESOS-1215 adds SET support, but for backwards compatibility we should fix the comparator operator first.