Add __getitem__ to Result class

[ogenstad]

Ran into an issue after the results was swapped out to an object.

(brigade3) ~/src/playground/brigade-tests/demo ᐅ python do.py
Traceback (most recent call last):
File "do.py", line 97, in
deploy()
File "do.py", line 89, in deploy
filtered.run(task=base_config)
File "/Users/patrick/src/forks/brigade/brigade/core/init.py", line 132, in run
result.raise_on_error()
File "/Users/patrick/src/forks/brigade/brigade/core/task.py", line 93, in raise_on_error
raise BrigadeExecutionError(self)
brigade.core.exceptions.BrigadeExecutionError: ok: {}, failed:{'switch00.cmh': TypeError("'Result' object is not subscriptable",), 'switch01.cmh': TypeError("'Result' object is not subscriptable",)}

[dbarrosop]

Yeah, that happened when I changed the result of the tasks to be an object instead of a dict. I am going to close this one because the API is not yet stable so I don't want to add a change for compatibility reasons. I am happy to discuss though if we want a dict or an object but that's a different topic so closing this one :)

Thanks!