Make entity_translation_translatable_batch() more drush friendly

This might be considered a sub-issue of #1800530: Drush Extension : Enable translation for Field translation, although it might also be useful for folks doing their own custom drush work. I've found that when invoking entity_translation_translatable_batch(), the memory usage for a field with many entries may spiral out of control. I believe this is because the operation uses entity_load() to load in the entities to process, which will keep loaded entities in a static variable. This is no problem when the function is ran through its intended use of the regular, http-request-based Batch API, but may become a problem when it is ran through e.g. drush.

This is easily remedied by passing a $reset to entity_load(). I will attach a patch for this shortly.