Honour deletionTimestamp for "kn revision delete", too

[rhuss]

As followup to #805 add the deletion timestamp handling also for kn revision delete.

[MIBc]

I want to continue working on it.

[rhuss]

/assign MIBc

[rhuss]

Yes, sorry for already merging the other PR but we are cutting a release today (0.14.0), so wanted to have your contribution to be included.

[MIBc]

Why we need to check deletionTimestamp for revision delete?
Unlike update command. Deleting revision will not hang until timeout. It may raise resource not found error if revision has been deleted.

[rhuss]

Not sure if I understand you comment correcly. Wouldn't it make sense to have consistent behaviour for deleting any resource ? I.e. if the thedeletionTimestamp is set then no deletion is attempt again (regardless of what we delete).