install: ensure iscsi service is running to handle shutdown properly
In some cases it is problematic to shutdown the iscsi targets (like raid over iscsi). Instead of introducing extra work to stop multi-layer storage devices during the install of curtin, this patch addresses the core issue around iscsi termination; ensuring the iscsi service is active prior to shutting down. In Artful, the open-iscsi service does not automatically start if iscsi configuration is not present during boot; curtin will restart/start the service if the storage configuration contains iscsi disks.
This approach successfully passes all of the iscsi configurations (plain, lvm over iscsi, and raid over iscsi).