Update tasks to log data to TurbiniaTaskResult

[aarontp]

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).

[aarontp]

Another way we could handle this is to create a custom log handler that saves the logs when logged via the normal logging mechanism and then attaches the logs logged for the given task to the result.

[aarontp]

This is already mostly done as the Tasks should be using TurbiniaTask.log(). This does python logging as well as save to TurbiniaResult so that they are later written as worker-log.txt. The last thing that needs to be done is to verify that all of the normal python logging calls are removed in favor of task.log(), so that we are not missing any logs in the saved worker log.