Either you have directly enabled some of the Red Hat Enterprise Linux 6
'optional' yum repositories on your system, or you have installed some packages
which have been moved from "base" to "optional" repository in Red Hat Enterprise
Linux 7.  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 RHEL 7 optional channel updated.  For this purpose, use
following additional option for redhat-upgrade-tool:

    --addrepo rhel-7-optional=<path to the optional repository>

Optionally, you could remove all packages which reside in RHEL 7 optional
repository before you start the system upgrade.