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  
These definitions, and the states below, should be defined as needed within each test function. That will help keep the relationship between each test and the config / state clear; for example:

```go
func TestMatch(t *testing.T) {
  var (
    config = newConfig(300, 2, map[string]string{"/a", "", "/b": ""})
  )
  // ...
  if !match(config, resources) {
    // ...
  }
}
```