Follow-up from "[#1960] added TKeyExchange class to handle TKEY exchange"

@fdupont :

Of course they are a lot of other (than timeout) errors to check. One is a bit particular to TKEY: you can't reuse the key name (so the test is to succeed with a key and to check failure using the same key name a second time. Of course the server must be prepared to refuse twice the same name. Perhaps we should first export a name generator method?).