Random fit algo

Implement and add unit tests for naive scheduling algorithm. First filter the agents to match the container configuration and than just randomly choose one. 

Constraints for now:
- cpu
- memory
- volumes

@peterbourgon @bernerdschaefer  @jmyounker  @soundcloud/iss  
I think instead of using this ok variable to set up the struct maps, it would make sense to use the toSet method you've defined.