Update to the new migration form in the single project view.
Before launching a project space migration (from the new form in the single project view), we ask for a user+ pwd and run the following test: We use the given user+pwd to run a "touch+rm" in the current project's space's data directory. In production, only ng6, root and users in the apache group can perform this action. (So only people with access to those credentials will be able tu run the switch_space_id workflow from there) More infos in the issue. Issue #129