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  
You can define variables within an if statement, which is perfect for this kind of thing:

```go
if expected, got := 0, len(unscheduled); expected != got {
  t.Fatalf()
}
```