Validate configuration before try to schedule it or run it on agent

* Validate configuration before try to schedule it or run it on agent. 
* Add prefix when making container id in scheduler, in order to ensure that container won't start with "-".
If the container id starts with "-", using the harpoonctl when inspecting the container will fail trying to parse the container id as argument.

@peterbourgon  @jmyounker  @stuartnelson3