[Satellite 6] Candlepin service is down after an upgrade to Satellite 6.9

Issue

• hammer ping shows that candlepin_events service is down after an upgrade to Satellite 6.9:

candlepin_events:
    Status:          FAIL
    message:         Not running
    Server Response: Duration: 0ms

• satellite-maintain health check reports:

Running ForemanMaintain::Scenario::FilteredScenario
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Check whether all services are running:                               [OK]
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Check whether all services are running using the ping call:           [FAIL]
Couldn't connect to the server: undefined method `to_sym' for nil:NilClass
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