Update tasks to log data to TurbiniaTaskResult

Right now a lot of the logging from the tasks does not get propagated back to the user, so we should make sure that all of the tasks are adding logs and errors to the results so that at minimum the data gets put into the worker-log.txt. Ideally we would store this info in datastore so that the clients could query it later (this part is in #115).

Start by locating TurbiniaTaskResult and the task implementations that produce worker output. Trace how task logs and errors reach worker-log.txt, then verify that each task adds this information to its result; datastore persistence is out of scope here and tracked in #115.

Written by the indexing model from the issue text.