check_grub_legacy: inhibit when GRUB legacy is present

[MichalHe]

Adds a new actor checking for whether any of the GRUB devices have the old GRUB Legacy installed. If any of such devices is detected, the upgrade is inhibited. The GRUB Legacy is detected by searching for the string 'GRUB version 0.94' in file -s of the device.

jira: RHEL-13342

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[MichalHe]

I have manually tested the patch, thus, the PR is ready for review.

[pirat89]

lgtm, we will need to just extend the report msg.

[pirat89]

The code works otherwise as expected. Tested on my upgraded 6 -> 7 system.

============================================================
                      REPORT OVERVIEW                       
============================================================

Upgrade has been inhibited due to the following problems:
    1. GRUB Legacy is used on the system
    ...

####
Risk Factor: high (inhibitor)
Title: GRUB Legacy is used on the system
Summary: Leapp detected GRUB Legacy to be installed on the system. The GRUB Legacy bootloader is unsupported on RHEL7 and GRUB2 should be used instead. GRUB Legacy has been detected on following devices:
/dev/vda

Related links:
    - How to install GRUB2 after a RHEL6 to RHEL7 upgrade: https://access.redhat.com/solutions/2643721
Remediation: [hint] Migrate to the GRUB2 bootloader on the reported devices.
Key: cb875a7c4a8d115b11659324aaca785f9e45ff72

[pirat89]

Updated results:

Risk Factor: high (inhibitor)
Title: GRUB Legacy is used on the system
Summary: Leapp detected GRUB Legacy to be installed on the system. The GRUB Legacy bootloader is unsupported on RHEL7 and GRUB2 must be used instead. The presence of GRUB Legacy is possible on systems that have been upgraded from RHEL 6 in the past, but required manual post-upgrade steps have not been performed. Note that the in-place upgrade from RHEL 6 to RHEL 7 systems is in such a case considered as unfinished.

GRUB Legacy has been detected on following devices:
/dev/vda

Related links:
    - How to install GRUB2 after a RHEL6 to RHEL7 upgrade: https://access.redhat.com/solutions/2643721
Remediation: [hint] Migrate to the GRUB2 bootloader on the reported devices. Also finish other post-upgrade steps related to the previous in-place upgrade, the majority of which is a part of the related preupgrade report for upgrades from RHEL 6 to RHEL 7.If you are not sure whether all previously required post-upgrade steps have been performed, consider a clean installation of the RHEL 8 system instead. Note that the in-place upgrade to RHEL 8 can fail in various ways if the RHEL 7 system is misconfigured.
Key: cb875a7c4a8d115b11659324aaca785f9e45ff72

I will try it yet on IBM Z arch (as I have it now by my hand) and in case tests pass, I am merging.

Update:
Tested manually following scenarious:

• legacy grub present (after IPU 6 -> 7): bios
• regression tests (i mean, no false positives raised):
  • grub2 rhel7 bios
  • grub2 rhel7 lvm
  • rhel 7 IBM Z

As actors are now present in el7toel8 repos and we do not expect this to be a valid case for IPU 8 -> 9, I did all testing just for IPU 7 -> 8.

Also, it's not expected to cover the detection for EFI boot as discussed internally due to capacities and very minor number of machines that actually upgraded from RHEL 6 to RHEL 7 using EFI boot.

[pirat89]

lgtm. I approved (and suggested) in this case to generate the report inside the factsphase. Consider it as an exception, as we are leaving slowly development for IPU 7 -> 8 and right now we have special circumstances. So let's do it in this way.

See my previous comment for more details about manual testing I did. CI tests passed.