Bug 1678634

Description of problem:

RHEL 8 fails to boot in a KVM (on a RHEL 7.6 Hypervisor) after customer's install script has run. It stops with the error message:
Failed to start Swtich Root

/sysroot is empty at this point. 

In rdsosreport.txt we have:

[    2.252419] gimp systemctl[543]: Failed to switch root: Specified switch root path '/sysroot' does not seem to be an OS tree. os-release file is missing.


Version-Release number of selected component (if applicable):
Red Hat Enterprise Linux 8

How reproducible:
This errors happens on 95% of all RHEL 8 installations in a KVM on customer's side.

Steps to Reproduce:
According to customer, steps to reproduce are:

1. install from RHEL 8 Snapshot 5 DVD
2. in anaconda manually configure the partitions to 
[root@elst ~]# df -Th
Filesystem                Type      Size  Used Avail Use% Mounted on
devtmpfs                  devtmpfs  8.3G     0  8.3G   0% /dev
tmpfs                     tmpfs     8.3G     0  8.3G   0% /dev/shm
tmpfs                     tmpfs     8.3G  8.7M  8.3G   1% /run
tmpfs                     tmpfs     8.3G     0  8.3G   0% /sys/fs/cgroup
/dev/mapper/root_vg-root  xfs        22G  4.8G   18G  22% /
/dev/mapper/oral_vg-oral  xfs       200G  1.5G  199G   1% /oral
/dev/mapper/orac_vg-orac  xfs       400G  2.9G  397G   1% /orac
/dev/mapper/home_vg-home  xfs       100G  747M  100G   1% /home
/dev/vda1                 xfs       994M  171M  824M  18% /boot
/dev/mapper/root_vg-var   xfs       9.8G  346M  9.5G   4% /var
/dev/mapper/root_vg-core  xfs       7.4G   85M  7.3G   2% /var/core
/dev/mapper/root_vg-log   xfs       9.8G  121M  9.7G   2% /var/log
/dev/mapper/root_vg-audit xfs       4.9G   69M  4.9G   2% /var/log/audit
tmpfs                     tmpfs     1.7G  4.0K  1.7G   1% /run/user/0
3. choose minimal installation (we have seen the error with other configurations too)
4. I also configured the time zone and the NIC, but this should be irrelevant
5. start the installation
6. you need access to the repositories:
rhel-8-for-x86_64-baseos-htb-rpms 
rhel-8-for-x86_64-appstream-htb-rpms 
codeready-builder-htb-for-rhel-8-x86_64-rpms
7. yum install perl-Net-Ping perl-URI
8. ./linux_trailer -A

Actual results:
The system cannot boot.

Expected results:
The system boots normally.

Additional info:
I'll attach the linux_trailer script and other config files to the bz.