Install from sdb fails if sda disk has a backup partition

[Ovidiu Poncea]

Brief Description
-----------------
AIO-SX was installed on sda then reinstalled on sdb resulted on failure.

Problem is that when anaconda install finds a backup partition on any disk that’s parsed earlier than the rootfs it skips creation of GPT partition tables on rootfs.
E.g. in this case there is a partition on /dev/sda as the system was installed earlier on that disk. Then when /dev/sda is parsed before /dev/sdb we detect the Platform Backup partition. This results in us skipping GPT table creation. This may work correctly if the disks are already GPT (therefore a wipedisk may hide this).

Severity
--------
Minor: This is a cornercase and, although system is unusable, workaround is simple and fix is persistent.

Steps to Reproduce
------------------
1. Install on sda - no need to run playbook
2. Reinstall on sdb

Expected Behavior
------------------
Anaconda installer completes

Actual Behavior
----------------
Anaconda fails

Reproducibility
---------------
100%

System Configuration
--------------------
AIO-SX

Test Activity
-------------
Evaluation

Workaround
----------
Wipe sda before install or in the installer once it fails and retry the install.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/736807

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/736807
Committed: https://git.openstack.org/cgit/starlingx/metal/commit/?id=de7bbcab26054dc950f3345228c319c0d5280e9b
Submitter: Zuul
Branch: master

commit de7bbcab26054dc950f3345228c319c0d5280e9b
Author: Mihnea Saracin <email address hidden>
Date: Thu Jun 18 20:37:45 2020 +0300

    Fix install from sdb if sda disk has a backup part

    Problem is when anaconda install finds a backup partition on any
    disk that’s parsed earlier than the rootfs, it skips the
    creation of GPT partition tables on rootfs.
    We fix this by checking the existence of
    the backup partition only on the rootfs disk.

    Closes-Bug: 1883844
    Change-Id: If2b473f24573f0dbcdadc0a4586c8be2c3185e75
    Signed-off-by: Mihnea Saracin <email address hidden>