Description of problem:

When upgrading satellite, we keep the old gem files in /usr/share/gems/gems which leaves a lot of crud behind on the filesystem. 

How reproducible:

Install a satellite 6.15 or earlier and upgrade it to the latest version and see old directories from gems left behind. 

Is this issue a regression from an earlier version:

No

Steps to Reproduce:

1. Install a 6.15 or earlier and upgrade it to the latest version

2. Check /usr/share/gems/gems and see old versions of katello, foreman and plugins

Actual behavior:
[root@satpreview gems]# ls | grep katello
hammer_cli_katello-1.17.0.pre.main
katello-4.16.0.pre.master
katello-4.17.0.pre.master

Expected behavior:
After an upgrade of a rubygem rpm we remove the old version since downgrades of satellite are not supported.