Controller: restore from backup can fail

[Tbaile]

Steps to reproduce

• Install nethsecurity-controller, add a second user and connect some units
• Run a backup of the controller
• Restore the backup on a node

Expected behavior

The restore completes and the restored controller has the same users, units and report data as the original one.

Actual behavior

The restore can fail due to a race condition, depending on whether the controller or the restore creates the database first.

Components

nethsecurity-controller 2.2.8