This appears to happen when the undercloud is not properly registered or has the appropriate available repositories.  Specifically in the output you can see:

This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
No package mysql-libs available.
No package mysql-devel available.

Because the system is not registered, the mysql-* items are not available and the installation fails.

It might be beneficial to add a preflight check to ensure that the undercloud has the appropriate repository resources available prior to installation but I'm not sure the best way to approach that.

As Mike, James and Alex mentioned, there is no bug, but it sounds more like a feature request, where we would check if repos are deployed before installing the undercloud.

Please file an RFE if that's the case and it will be worked by the DFGs.
Also feel free to re-open this bug in case I missed something.

(In reply to Emilien Macchi from comment #13)
> As Mike, James and Alex mentioned, there is no bug, but it sounds more like
> a feature request, where we would check if repos are deployed before
> installing the undercloud.
> 
> Please file an RFE if that's the case and it will be worked by the DFGs.
> Also feel free to re-open this bug in case I missed something.

Just to add; we identified this to be a bug in yum and we fixed it in 7.4, see:
https://bugzilla.redhat.com/show_bug.cgi?id=1352585#c4