MDL-36963 Improve mdeploy worker::move_directory() method
MDL-36963 Improve mdeploy worker::move_directory() method

The additional parameter allows to use this method without actual
removing the root of the source location. That is, it is now possible to
move the content of a folder only.

Also, a small refactoring happened here as we will need a variant of
this method that does not throw exception if the target already exists.

dilawar/moodle