Support auto generation of the log folders

[mgriff]

When running the migration I don't want to have to set the log folder each time, I end up using a numbering system (i.e. run1, run2, run3) which doesn't add much value.

I propose we add an option to use a default folder path, initially still using the output-folder parameter but potentially making it the default in the future.

I propose we use the following format: logs/<cloud_name>/<todays_date>/<current_time>