Description of problem:
Anaconda crashes if there is software RAID already exist in the disks (An unknown error has occurred)

Version-Release number of selected component (if applicable):
33.16.4.15-1.el8

How reproducible:
Always.

Steps to Reproduce:
1. Create the software raid by mdadm via the rescue mode or any other bootable Linux media.
2. Reboot the machine.
3. Start the Anaconda installer.

Actual results:
Anaconda will crash at the language selection page.

Expected results:
No crashes at all.

Additional info:
Reproducible in RHEL 8.3-8.4. RHEL 8.0-8.2 has a slightly different result, which lead to a black screen and no Anaconda GUI shows up at all. RHEL 7.x and Fedora 34 seems OK.