Description of problem:
Hammer allows adding an erratum to a content view filter even if the packages updated by the erratum are not available from any repositories in the content view.
Steps to Reproduce:
1. Create a content view with only the rhel-6-server-rpms and rhel-6-server-satellite-tools-6.3-rpms repositories
2. Create a yum content filter on the content view including all available errata updated in 2018
3. Add RHSA-2018:3665 (which only applies to RHEL 7 and was not available in the previous step) using hammer:
# hammer content-view filter rule create --content-view-filter-id 1 --errata-id RHSA-2018:3665
RHSA-2018:3665 is visible in the RHEL 6 content view filter errata list using both the Satellite webUI and `hammer content-view filter info`.
Hammer does not allow a user to add a given erratum to a content view filter unless packages affected by that erratum are available in the content view. Hammer presents an error when a user attempts to add such an erratum to a filter.