[BUG] `OSpackages.sh` script's `-g` Feature Does Not Properly Handle Groups Other Than `core`

[ferricoxide]

Describe the bug

If attempting to use a different yum RPM-group to build an other-than-core image, the OSpackages.sh script will fail.

Expected behavior

Custom builds using arbitrary repository-defined RPM-groups other than the @core group should work

Deviance Description

Custom builds using arbitrary repository-defined RPM-groups other than the @core group does not work