Description of problem:

The current default behavior of yum4/dnf is skip_if_unavailable=True.  This default behavior is being changed to False on bz1679509.  

While one can manually set change this parameter setting in each individual repository file, it is also desired to have a global configuration setting as well so that repository configurations that do not have a behavior defined will default to False in order to be as safe as possible.  Presumeably this parameter would be defined in /etc/yum.repos.d/{yum, dnf}.conf

Background reasoning:
With a default behavior of yum4/dnf is skip_if_unavailable=True, dnf will log messages that a repository is unavailable, but continue with changes for other repositories that are available.

This could cause scripts to appear as though they have succeeded when in fact the repo is unavailable. Install, search, or update  operations will result in a return code of 0. Again, this occurs only if the desired repo is unavailable. 

Users may incorrectly assume that security errata was applied, or that complex layered applications such as openstack were updated as a complete state along with the OS, when in fact some repositories might have been unavailable.

This could be seen as a behavioral regression to prior releases of yum-3 in RHEL 7 and earlier.


Workaround: 
As a workaround one can add "skip_if_unavailable=False" to each of the BaseOS and AppStream repository entries in the /etc/yum.repos.d/redhat.repo file. This results in the behavior seen with yum3 on RHEL 7.