Include btrfs-progs for btrfs filesystem support

[dcasota]

Add btrfs-progs to install list for btrfs partitions.

[oliverkurth]

Did you see any problem with btrfs-progs not installed?

[dcasota]

Yes. btrfs-progs isn't in packages_minimal.json (or packages_developer.json), so it isn't pulled in transitively — a minimal install onto btrfs boots with no btrfs userspace tooling at all (btrfs, fsck.btrfs, the 64-btrfs.rules udev rules).

mkfs.btrfs at install time is fine — that runs in the installer initrd. The gap is the resulting target system, which then can't:

• run fsck.btrfs (referenced via the fstab pass number at boot),
• btrfs device scan / assemble multi-device or labeled volumes (the udev/initramfs path), or
• manage the btrfs subvolumes the installer itself can create (subvol= fstab entries) — there's no btrfs binary to snapshot/scrub/check/repair.

This mirrors the existing lvm2 line just above: when a partition uses a storage feature, the installed system needs that feature's tools. The addition is guarded by if any(p.get('filesystem') == 'btrfs' for p in partitions), so it only pulls in btrfs-progs when btrfs is actually selected.

(For reference, this change is also carried as a downstream spec patch in vmware/photon#1658 for the 5.0 build.)