aaa_base's get_kernel_version was fixed for .xz images, instead of failing it
returns the proper kernel version now.

On i586 this breaks mkinitrd though. For i586, it currently uses the "vmlinu."
regex for getting the kernel binaries in /boot, which also matches
/boot/vmlinux-...-....xz, which isn't the bootable kernel. Until now, those
were ignored because get_kernel_version failed.

Now that get_kernel_version is fixed, it now tries to build an initrd for the
".xz" versions, which obviously fails.

The fix is simple: Use i?86|x86_64) as match instead of i386|x86_64) in line
174.

## Observation

openQA test in scenario opensuse-Tumbleweed-DVD-i586-textmode@32bit fails in
[await_install](https://openqa.opensuse.org/tests/1221153/modules/await_install/steps/11)

## Test suite description
Maintainer: okurz

Installation in textmode and selecting the textmode "desktop" during
installation.


## Reproducible

Fails since (at least) Build
[20200330](https://openqa.opensuse.org/tests/1219967)


## Expected result

Last good: [20200329](https://openqa.opensuse.org/tests/1218352) (or more
recent)


## Further details

Always latest result in this scenario:
[latest](https://openqa.opensuse.org/tests/latest?arch=i586&distri=opensuse&flavor=DVD&machine=32bit&test=textmode&version=Tumbleweed)