[Bug] Replace send_pickled in CARLA drivers

[mageofboy]

send_pickle is deprecated in erdos. These changes replace the functionality of send_pickle by unpickling the message then using the standard send method. This is necessary for when running the pseudo-asynchronous simulator mode.

[pschafhalter]

Good catch, and thanks for the PR!

It looks like storing pickled messages in these operators is redundant -- we can just stores messages directly. Could you update the PR to make that change? Concretely:

1. Rename _pickled_messages to _messages.
2. Don't pickle the messages. Instead, do self._messages[msg.timestamp] = msg

[ICGog]

We we're doing this in order to move the pickling of large sensor messages from the critical the critical path. If we stop pre-pickling messages, and sending them using the send_pickle method then the long pickling time will be accounted in the end-to-end response time, affecting experiments.

[pschafhalter]

Hmmm, maybe we need to re-introduce this function in ERDOS.

I was under the impression that pickling a message took a negligible amount of time, but serializing a (1920, 1080, 3) numpy array takes around 15 ms on my laptop.

[ICGog]

Yes, I think it would be good to re-introduce this function for now in order to ensure that the driver operators do not affect our experiments.