assert: EventuallyWithT must catch panics in condition such as CollectT.FailNow

[dolmen]

In EventuallyWithT the condition function may call CollectT.FailNow which panics.

The implementation of EventuallyWithT should catch this panic (as well as any other panic in the condition).

[dolmen]

Cc: @brackendawson @czeslavo @cszczepaniak

[dolmen]

CollectT.FailNow is required to be able to use functions from package require. I think we should use a sentinel value in the panic to handle that panic specifically.