chore: fix probe log when response if empty

[stehessel]

Description

Prevent the () in log when the Central response is empty.

E0904 10:29:57.650706 1 probe.go:103] could not list centrals: : Get "https://api.integration.openshift.com/api/rhacs/v1/centrals": context deadline exceeded
W0904 10:29:57.650759 1 runtime.go:44] cleanup failed: cleanup centrals failed: retry failed: context deadline exceeded: probe run failed: creation of central instance failed: parsing HTTP response: undefined response type
I0904 10:29:57.650781 1 probe.go:69] probe run has been started: fleetManagerEndpoint="https://api.integration.openshift.com/", provider="aws", region="us-east-1"
I0904 10:29:57.661891 1 probe.go:147] creation of central instance () requested
I0904 10:29:57.661931 1 probe.go:54] elapsed time: 11.143458ms
I0904 10:29:57.661946 1 probe.go:79] probe run has ended

Compared to healthy one:

I0904 09:49:37.082595 1 probe.go:127] finished clean up attempt of probe resources
I0904 09:49:37.082638 1 probe.go:69] probe run has been started: fleetManagerEndpoint="https://api.stage.openshift.com/", provider="aws", region="us-east-1"
I0904 09:49:37.331281 1 probe.go:147] creation of central instance (cjqqgcdib723trpqgtag) requested
I0904 10:01:07.349105 1 probe.go:212] central instance cjqqgcdib723trpqgtag is in "ready" state
I0904 10:01:12.430202 1 probe.go:176] deletion of central instance cjqqgcdib723trpqgtag requested
I0904 10:02:02.438883 1 probe.go:235] central instance cjqqgcdib723trpqgtag has been deleted
I0904 10:02:02.438911 1 probe.go:54] elapsed time: 12m25.356266322s
I0904 10:02:02.438923 1 probe.go:86] probe run has ended

Also added a dedicated log statement when the probe fails, so we don't have to wait until the cleanup is done (which may also fail and retry).

[openshift-ci]

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This pull-request has been approved by: porridge, stehessel

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