[OSPRH-9371] Fix VerifySecret so it requeues when necessary

[abays]

We've come to realize three things recently:

1. Returning an error to the reconciler along with a RequeueAfter will cause the reconciler to abandon the explicit requeue and only consider the error [1].
2. The VerifySecret function in lib-common was returning an error along with a requeue, thus contributing to the problem listed in item 1. [2]
3. Also, the error VerifySecret was returning was not a "not found" error, but a generic k8s error -- so it wouldn't be properly handled by callers looking for a "not found" error. [3]

Now VerifySecret only returns a non-empty ctrl.Result{} if the Secret is missing, so let's handle that case in a separate if-clause. [4]

Jira: https://issues.redhat.com/browse/OSPRH-9371

[1] https://github.com/openstack-k8s-operators/keystone-operator/pull/459 [2] https://github.com/openstack-k8s-operators/lib-common/blob/ad3edb6e67ab738cfdbf4e2e78ac403784a08ab7/modules/common/secret/secret.go#L423-L425 [3] https://github.com/openstack-k8s-operators/lib-common/blob/ad3edb6e67ab738cfdbf4e2e78ac403784a08ab7/modules/common/secret/secret.go#L425 [4] https://github.com/openstack-k8s-operators/lib-common/blob/579da98fa7a62b70b43cdba92e82d6497afe8835/modules/common/secret/secret.go#L425-L427

[openshift-ci[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: abays, stuggi

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[abays]

/cherry-pick 18.0.0-proposed

[openshift-cherrypick-robot]

@abays: #149 failed to apply on top of branch "18.0.0-proposed":

Applying: Fix VerifySecret so it requeues when necessary
Using index info to reconstruct a base tree...
M   api/go.mod
M   api/go.sum
M   controllers/barbicanapi_controller.go
M   go.mod
M   go.sum
Falling back to patching base and 3-way merge...
Auto-merging go.sum
CONFLICT (content): Merge conflict in go.sum
Auto-merging go.mod
CONFLICT (content): Merge conflict in go.mod
Auto-merging api/go.sum
Auto-merging api/go.mod
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 Fix VerifySecret so it requeues when necessary
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to [this](https://github.com/openstack-k8s-operators/barbican-operator/pull/149#issuecomment-2358498331): >/cherry-pick 18.0.0-proposed Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes-sigs/prow](https://github.com/kubernetes-sigs/prow/issues/new?title=Prow%20issue:) repository.