Either you have directly enabled some of the OL6
'optional' yum repositories on your system, or you have installed some packages
which have been moved from "base" to "optional" repository in OL7.
This will very likely cause fail during upgrade of your system.

Please, provide additional yum repository to redhat-upgrade-tool to make
packages residing in OL7 optional channel updated.  For this purpose, use
following additional option for redhat-upgrade-tool:

    --addrepo ol7_optional_latest=<path to the optional repository>

Optionally, you could remove all packages which reside in OL6 optional
repository before you start the system upgrade.
