Can't configure persistent volume on Jessie

Originally created by @intrigeri on #10809 (Redmine)

Started 2.0~beta1 with a persistence volume activated, “Configure persistent volume” => I’m told “Persistence volume is not writable. Maybe it was mounted read-only?”.

Feature Branch: bugfix/persistence-fixes-for-2.0-take1

Related issues

Related to #10834 (closed)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information