AgentRunner : exception handling

[planetf1]

          We need a generic way to deal with exceptions. Right now it seems like you are just passing the exception to the caller. 

That’s one approach. Another approach to think about is an exception handler. So something like:

class AbstractAgent(ABC):
  #…
  def exception_handler(self, handler) -> error:
     pass
  #…

We can then let the handler object be defined and passed by the caller. This will allow exceptions to be handled by caller of the runner. For instance if there was a policy to retry.

Also if the handler is not defined then by default the exception is propagated up as you are doing now.

Originally posted by @maximilien in #125 (comment)

[maximilien]

I think this is duplicate to #112