Howdy,

I found out that there is new Red Hat branding in yum.

1. Get newest yum.
2. Move all repos to different location (probably enable=0 also would
work - not tested), and disable any other repo (if there is repo enabled
from another sources/plugin).
3. Try to update the system.

One-liner: "sudo yum update yum -y && mkdir repos && sudo mv
/etc/yum.repos.d/* repos/. && sudo yum update"

yum update returns:
"""
There are no enabled repos.
 Run "yum repolist all" to see the repos you have.
 To enable Red Hat Subscription Management repositories:
     subscription-manager repos --enable <repo>
 To enable custom repositories:
     yum-config-manager --enable <repo>
"""

Patch responsible for change: BZ-1175309-enable-repos-instruction.patch

This patch has number 230 in spec file.

Bests,
Alex

PS. http://ftp.scientificlinux.org/linux/scientific/7.4/SRPMS/SL/
doesn't contain current yum version. yum.ini from
http://ftp.scientificlinux.org/linux/scientific/7.4/SRPMS/vendor/yum-3.4.3-154.el7.src.rpm
states that yum should be sl7, but yum from
http://ftp.scientificlinux.org/linux/scientific/7.4/x86_64/os/Packages/
is el7.