Command create-site-skeletons-container should use parent location id 1 as default.

Context: Upgrading from v3.0 to v3.1

By default, when the parameter -p, --parent-location-id[=PARENT-LOCATION-ID] is omitted, location ID 2 is used. (screen-shot 1) This means the "Welcome to eZ Platform Enterprise Edition" landing page is used as parent.

On a fresh v3.1 installation (when not upgrading) the "Site skeletons" folder container is located under root with location ID 1. (screen-shot 2)

Unless the skeletons container is located under location ID 1 the Content Tree view for Admin / Site skeletons is not displayed correctly. (screen-shot 3) Despite setting the correct id in ezplatform.system.<SCOPE>.site_factory.site_skeletons_location_id and under content_tree_module.contextual_tree_root_location_ids.

Remarks: One could argue that the parameter allows setting different ids however most users won't be aware of this and will end up with unexpected results.