Package constraint has functions for ensuring that collections of containers are allowed to run together on a single host.
TODO: Add resource math. Phrase this code in a way that makes it easy to call from schedulers as well as from the feasiblity check that apiserver performs.
Allowed returns true if pods is a collection of bound pods which can run without conflict on a single minion.
PortsConflict returns true iff two containers attempt to expose the same host port.