fix: display-name api call on non-existing client

[DuckBoss]

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Complete Description of Additions/Changes:

This patch changes the display-name update logic to not attempt to set the display-name from the insights-client config when the system is not confirmed to be registered to HBI.

Resolves: CCT-173, BZ#2192510

[candlepin-bot]

Can one of the admins verify this patch?

[DuckBoss]

Closing this card as the original issue seems to have been resolved in server-side changes.