Documentation for yum groups

The System Admin documentation for RHEL7, specifically the section on working with yum groups, should include troubleshooting step(s) for when the information in yum groups and rpmdb is out of sync for some reason.

Previously, such issues would result in yum transaction errors that would provide the user with commands to rectify the situation. I'm not sure that's still the case, but the previous commands and advice should be documented in this appropriate part of the documentation.