I was trying to re-install a previously installed BIOS system, where the disk uses the msdos partition table and not having the biosboot partition.

The mount point assignment option was disabled because:
"Some required partitions are missing: BIOS Boot"

Since the disk uses the msdos partition table, it is not necessary to create the biosboot partition. As a confirmation, the older GTK interface allows to reuse the existing disk layout without having to create the biosboot partition.

Reproducible: Always

Steps to Reproduce:
1. Have a previously installed BIOS system having the msdos partition table and not having the biosboot partition.
2. Try to reinstall the system using the mount point assignment option in WebUI.
Actual Results:  
The mount point assignment option was disabled because:
"Some required partitions are missing: BIOS Boot"

Expected Results:  
Allow to assign the existing partitions and finish the installation.