Description of problem:
When using `dnf repolist` or `dnf update` from RHEL8 client registered to Satellite 5.8 it fails with
~~~
Failed to synchronize cache for repo 'rhel-x86_64-baseos-8-htb'
~~~

Version-Release number of selected component (if applicable):
# rpm -qa | grep satellite
~~~
satellite-branding-5.8.0.9-1.el6sat.noarch
satellite-repo-5.8.0.2-2.el6sat.noarch
satellite-schema-5.8.0.48-1.el6sat.noarch
satellite-doc-indexes-5.8.0-1.el6sat.noarch
~~~

# rhn-schema-version 
~~~
5.8.0.48-1.el6sat
~~~

How reproducible:
100%

Steps to Reproduce:
1. Sync rhel8 HTB channel 
2. Register RHEL8 HTB system to Satellite 5.8
3. `dnf repolist` or `dnf update`


Actual results:
~~~
# dnf repolist --debuglevel=10

timer: config: 5 ms
Loaded plugins: builddep, config-manager, copr, debug, debuginfo-install, download, generate_completion_cache, needs-restarting, playground, product-id, repoclosure, repodiff, repograph, repomanage, reposync, spacewalk
initialized Spacewalk plugin
This system is receiving updates from Spacewalk server.
{'rhel-x86_64-baseos-8-htb': {'type': 'up2date', 'url': ['https://ktordeur-sat58.usersys.redhat.com/XMLRPC'], 'gpg_key_url': 'file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-beta file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release', 'description': 'Red Hat Enterprise Linux - BaseOS High Touch Beta (v. 8 for AMD64 / Intel64)', 'org_id': '', 'label': 'rhel-x86_64-baseos-8-htb', 'version': '20190108130028', 'local_channel': '0', 'parent_channel': '', 'summary': 'Red Hat Enterprise Linux BaseOS High Touch Beta (v. 8 for AMD64 / Intel64)', 'arch': 'channel-x86_64', 'id': '150', 'name': 'RHEL BaseOS HTB (v. 8 for x86_64)'}, 'rhel-x86_64-appstream-8-htb': {'type': 'up2date', 'url': ['https://ktordeur-sat58.usersys.redhat.com/XMLRPC'], 'gpg_key_url': 'file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-beta file:///etc/pki/rpm-gpg/RPM-GPG-KEY-redhat-release', 'description': 'Red Hat Enterprise Linux - AppStream High Touch Beta (v. 8 AMD64 / Intel64', 'org_id': '', 'label': 'rhel-x86_64-appstream-8-htb', 'version': '20190108131157', 'local_channel': '0', 'parent_channel': '150', 'summary': 'Red Hat Enterprise Linux AppStream High Touch Beta (v. 8 AMD64 / Intel64)', 'arch': 'channel-x86_64', 'id': '151', 'name': 'RHEL AppStream HTB (v. 8 for x86_64)'}}
DNF version: 4.0.9
Command: dnf repolist --debuglevel=10 
Installroot: /
Releasever: 8
cachedir: /var/cache/dnf
Base command: repolist
Extra commands: ['repolist', '--debuglevel=10']
RHEL BaseOS HTB (v. 8 for x86_64)                                                                                                                                                  0.0  B/s |   0  B     00:01    
RHEL AppStream HTB (v. 8 for x86_64)                                                                                                                                               0.0  B/s |   0  B     00:01    
Failed to synchronize cache for repo 'rhel-x86_64-baseos-8-htb', ignoring this repo.
Failed to synchronize cache for repo 'rhel-x86_64-appstream-8-htb', ignoring this repo.
~~~


Expected results:

`dnf repolist` and `dnf update` to work

Additional info:

Repodata generation finished:
~~~
# grep rhel-x86_64-baseos-8-htb /var/log/rhn/rhn_taskomatic_daemon.log

INFO   | jvm 1    | 2018/12/07 16:46:00 | 2018-12-07 16:46:00,093 [Thread-10484] INFO  com.redhat.rhn.taskomatic.task.repomd.RepositoryWriter - Generating new repository metadata for channel 'rhel-x86_64-baseos-8-htb'(sha256) 2240 packages, 0 errata
INFO   | jvm 1    | 2018/12/07 16:46:52 | 2018-12-07 16:46:52,745 [Thread-10484] INFO  com.redhat.rhn.taskomatic.task.repomd.RepositoryWriter - Repository metadata generation for 'rhel-x86_64-baseos-8-htb' finished in 52 seconds
~~~