Rename the `start` method to `run` as this is what is what is called
by the threading module's `start` method, otherwise this causes the
polling to be done in the main thread blocking execution.
- Workload's update_result stage has now been broken up into two parts:
extract_results and update_output. This is to allow the assistant to
pull output from the target in between the two stages.
- Updated assistant implementations for Linux and Android targets from
the exisiting code.
- Extended target descriptor code to handle assistants and their
parameters as well.
- Updated the target manager to actually make use of the assistants.
