Description of problem:
I wanted create Fedora channel with synced packages from fedora's repository

https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64

I received error and no packages were synced

ERROR: File /var/cache/rhn/reposync/1/External Fedora 25/metalink.xml does not exist

I tried same task on Satellite 5.7 and older version works good
spacewalk-backend-tools-2.3.3-45.el6sat.noarch

It looks that it is regression. 

Version-Release number of selected component (if applicable):
spacewalk-backend-tools-2.5.3-48.el6sat.noarch

How reproducible:
always

Steps to Reproduce:
1. create channel and add custom repository (https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64)
2. try to sync repo by webui and look at log with result

Actual results:
= Satellite 5.8 =
2017/01/06 15:16:06 +03:00 Command: ['/usr/bin/spacewalk-repo-sync', '--channel', 'fedora25-x86_64', '--type', 'yum', '--latest', '--sync-kickstart']
2017/01/06 15:16:06 +03:00 Sync of channel started.
2017/01/06 15:16:06 +03:00 Repo URL: https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64
2017/01/06 15:16:11 +03:00 ERROR: File /var/cache/rhn/reposync/1/External Fedora 25/metalink.xml does not exist
2017/01/06 15:16:11 +03:00 ERROR: File /var/cache/rhn/reposync/1/External Fedora 25/metalink.xml does not exist
2017/01/06 15:16:11 +03:00 Sync of channel completed in 0:00:05.


Expected results:
= Satellite 5.7 =
['/usr/bin/spacewalk-repo-sync', '--channel', 'fedora-25-x86_64', '--type', 'yum', '']
Repo URL: https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64
Packages in repo:             51669
Packages passed filter rules:     3
Packages already synced:          0
Packages to sync:                 3
1/3 : kernel-modules-4.8.6-300.fc25-0.x86_64
2/3 : kernel-core-4.8.6-300.fc25-0.x86_64
3/3 : kernel-4.8.6-300.fc25-0.x86_64
Linking packages to channel.
Repo https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64 has comps file df2eae999a4f7c464b743a16f112f1b3c039dc945c305578195524f83fb66833-comps-Everything.x86_64.xml.gz.
Repo https://mirrors.fedoraproject.org/metalink?repo=fedora-25&arch=x86_64 has 0 errata.
Sync completed.
Total time: 0:00:21