shell: Disable chunk size for RAID 1

Disable the selectpicker for RAID 1
Show the text "0 KB" for RAID 1
Set the chunk size to 0 when creating RAID devices

Fixes #1071
Closes #1089
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
 * Hide the chunk row, don't dig into selectpicker internals.