Create config option to deal with the order of Entity Managers.

[otaviofff]

If your application has to deal with multiple Entity Managers (EMs), such as one per application module, then you should be able to define the order in which each EM has to be executed, so that things like database referential integrity can be taken into account.

This is especially desirable for CLI scripts, which will have to iterate through multiple EMs and execute a given fuction, such as database reset (drop schema + create schema).