Legacy boot flag in proposal

[ancorgs]

Depends on the discussion at https://trello.com/c/RAPZuM0j/640-3-storageng-bootloader-bootloader-does-not-detect-prep-boot-partition

If we conclude that the legacy boot must be set for PReP, this PR should do it. Otherwise, this can be closed right away.

[coveralls]

Coverage increased (+0.03%) to 59.875% when pulling 0bb19ef on ancorgs:legacy_boot into 2329bd2 on yast:master.

[ancorgs]

The conclusion is that we should solve the original problem in three places:

• Bootloader should not "overcheck". That's already addressed in do not complain for ppc and gpt when nothing is activated yast-bootloader#448, which should be enough to make the installation succeed.
• PartitionCreator should be adapted to:
  • never touch the legacy_boot flag in PPC
  • treat that flag in the same way than the MBR boot flag (that is, honoring Planned::Partition#bootable like suggested in this PR) in other architectures.
• To make things more clear in BootRequirementsChecker (specially in the RSpec tests we are using to discuss stuff), we should adapt it to never propose #bootable == true for a PReP planned partition within a GPT disk.

So I will modify this PR to cover the last two points.

[wfeldt]

To clarify this legacy_boot flag in GPT which grub2 sets, here is the relevant part of the UEFI spec:

UEFI Spec 2.6

5.3.3 GPT Partition Entry Array

Attribute, Bit 2 (Legacy BIOS Bootable)

This bit is set aside by this specification to let systems with traditional PC-AT BIOS firmware implementations inform certain limited, special-purpose software running on these systems that a GPT partition may be bootable.

['certain limited, special-purpose software' here means syslinux mbr]

GPT just doesn't have a 'bootable' flag.. Instead it uses dedicated partition (gu)ids to indicate partitions to use for booting. Like for prep or efi-bios. So it's enough to have a prep partition, you don't need to tag it specially for booting.

[teclator]

@ancorgs this PR is probably out of date, and taking in account how fat storage-ng has been changing maybe it does not make sense anymore.

Could you check it and close if it is not needed.

[ancorgs]

Too old.