Description of problem:
Unable to upgrade content host from 6.2 to 6.3 using Satellite 6.3 UI

Version-Release number of selected component (if applicable):
satellite - satellite-6.3.1-3.el7sat.noarch
Client (6.2.z):
katello-host-tools-3.0.2-1.el7sat.noarch
katello-agent-3.0.2-1.el7sat.noarch
katello-host-tools-fact-plugin-3.0.2-1.el7sat.noarch
pulp-rpm-handlers-2.8.7.16-1.el7sat.noarch
python-pulp-common-2.8.7.18-1.el7sat.noarch
python-pulp-rpm-common-2.8.7.16-1.el7sat.noarch
python-pulp-agent-lib-2.8.7.18-1.el7sat.noarch

How reproducible:
Always

Steps to Reproduce:
1. Upgrade Satellite (and capsules) from 6.2.z to 6.3. Clients still use 6.2 Satellite Tools.
2. Client upgrade documentation https://access.redhat.com/documentation/en-us/red_hat_satellite/6.3/html/upgrading_and_updating_red_hat_satellite/upgrading_red_hat_satellite#upgrading_clients states to install `satellite-6.3-tools-upgrade` package and update `katello-agent` package from Satellite UI -> Hosts  -> Content Hosts -> Select Action -> Manage Packages

Actual results:
After the above-mentioned step is performed, the clients started throwing an error (see attachment) in /var/log/messages and the package updates did not happen.

Expected results:
1. Either the package management from Satellite 6.3 should work on the 6.2 tools Client (or)
2. The doc should be updated to remove this method from the recommended steps. This would leave the user with Remote Execution or manual pull from the client to upgrade to 6.3

Additional info: