Cannot upgrade RHEV due 'Preparing CA... [ ERROR ]'

Issue

I'm not able to upgrade RHEV. Running rhevm-upgrade, the process fails in the "Preparing CA" step:

...

Stopping ovirt-engine service...                     [ DONE ]
Stopping DB related services...                      [ DONE ]
Cleaning async tasks...                              [ DONE ]
Pre-upgrade validations...                           [ DONE ]
Backing Up Database...                               [ DONE ]
Rename Database...                                   [ DONE ]
Updating rpms...                                     [ DONE ]
Updating Database...                                 [ DONE ]
Restore Database name...                             [ DONE ]
Preparing CA...                                      [ ERROR ]

 **Error: Upgrade failed, rolling back**
 **Reason: Error: failed updating configuration field keystoreUrl to /etc/pki/ovirt-engine/keys/engine.p12**

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