Entity created time should be part of the row key of entity table

Entity created time should be part of the row key of entity table, between entity type and entity Id. The reason to have it is to index the entities. Though we cannot index the entities for all kinds of information, indexing them according to the created time is very necessary. Without it, every query for the latest entities that belong to an application and a type will scan through all the entities that belong to them. For example, if we want to list the 100 latest started containers in an YARN app.