Fix error logs with stale success message

[darkowlzz]

Depends on fluxcd/pkg#511.

Due to a bug in reconcile ResultFinalizer, the Ready=True condition on
an ImageRepository object from the previous reconciliation wasn't
getting updated even when the reconciliation failed, for example due to
image scan failure.

When the ResultFinalizer receives an object with stale Ready=True with
message "successful scan: found x tags" from the previous successful
reconciliation, Reconciling=True to indicate in-progress reconciliation
and a reconciliation error, ResultFinalizer updates Ready value if it's
True. But the check was performed using conditions.IsReady() which
also takes into consideration the Reconciling and Stalled values in the
status. Due to the presence of Reconciling=True, even though Ready was
True, conditions.IsReady() returned False, and ResultFinalizer skips
updating the Ready value, resulting in a fully reconciled final object
status with Reconciling and Ready both True, which is an incorrect
reconciliation status result.
ResultFinalizer now uses conditions.IsTrue(obj, meta.ReadyCondition)
to precisely check if only Ready=True is present.

Also, remove ExternalEventRecorder from ImageRepositoryReconciler, which
is no longer used and add a missing return on progressive status
patching failure.

In addition, update tests to use condition checker with gomega WithT()
for proper assertion failure and stacktrace.

Refer #356