Upgrade of Red Hat Satellite 6.2 to 6.3 errors in clean_backend_objects step due to candlepin 503 error

Issue

foreman-maintain upgrade run --target-version 6.3 errors with the following:

[ INFO 2018-12-05 19:26:11 main] Upgrade Step: clean_backend_objects (this may take a while) ...
[DEBUG 2018-12-05 19:26:31 main] rake aborted!
[DEBUG 2018-12-05 19:26:31 main] RestClient::ServiceUnavailable: Katello::Resources::Candlepin::Consumer: 503 Service Unavailable {"displayMessage":"Candlepin is in Suspend mode, please check /status resource to get more details","requestUuid":"828adc6f-820e-4a31-8e3c-8a7b2f629105"} (GET /candlepin/consumers/?owner=SomeOrg&include=uuid&per_page=15000&page=1)
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/abstract_response.rb:223:in `exception_with_response'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/abstract_response.rb:103:in `return!'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/request.rb:860:in `process_result'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/request.rb:776:in `block in transmit'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/request.rb:766:in `transmit'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/request.rb:215:in `execute'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/request.rb:52:in `execute'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/rest-client-2.0.0/lib/restclient/resource.rb:51:in `get'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/http_resource.rb:84:in `get'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:147:in `block in get'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:102:in `block in fetch_paged'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:100:in `loop'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:100:in `fetch_paged'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:146:in `get'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:135:in `block in all_uuids'
[DEBUG 2018-12-05 19:26:31 main] /opt/rh/rh-ror42/root/usr/share/gems/gems/activerecord-4.2.6/lib/active_record/relation/delegation.rb:46:in `map'
[DEBUG 2018-12-05 19:26:31 main] /opt/rh/rh-ror42/root/usr/share/gems/gems/activerecord-4.2.6/lib/active_record/relation/delegation.rb:46:in `map'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/app/lib/katello/resources/candlepin.rb:134:in `all_uuids'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/lib/katello/tasks/clean_backend_objects.rake:13:in `populate!'
[DEBUG 2018-12-05 19:26:31 main] /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.4.5.87/lib/katello/tasks/clean_backend_objects.rake:100:in `block (2 levels) in <top (required)>'
[DEBUG 2018-12-05 19:26:31 main] Tasks: TOP => katello:clean_backend_objects
[DEBUG 2018-12-05 19:26:31 main] (See full trace by running task with --trace)
[ERROR 2018-12-05 19:26:31 main] foreman-rake katello:clean_backend_objects COMMIT=true failed! Check the output for error!
[ERROR 2018-12-05 19:26:31 main] Upgrade step clean_backend_objects failed. Check logs for more information.
[DEBUG 2018-12-05 19:26:31 main] Exit with status code: 1 (signal was 1)
[ERROR 2018-12-05 19:26:31 main] Errors encountered during run:
[ERROR 2018-12-05 19:26:31 main] foreman-rake katello:clean_backend_objects COMMIT=true failed! Check the output for error!
[ERROR 2018-12-05 19:26:31 main] Upgrade step clean_backend_objects failed. Check logs for more information.
[DEBUG 2018-12-05 19:26:31 main] Cleaning /tmp/kafo_puppet20181205-2721-7cbfwm.conf
[DEBUG 2018-12-05 19:26:31 main] Cleaning /tmp/kafo_hiera20181205-2721-1gp5do
[DEBUG 2018-12-05 19:26:31 main] Cleaning /tmp/kafo_puppet20181205-2721-13n6s52.conf
[DEBUG 2018-12-05 19:26:31 main] Cleaning /tmp/default_values.yaml
[ INFO 2018-12-05 19:26:31 main] Installer finished in 3242.998938642 seconds