E2E: Broker config test failing

[Haarolean]

          @Haarolean hey, I've faced failed brokersConfigEditCheck at this PR

and while investigation really reproduced it locally. it's not because of test :)

Possibly a bug

Brokers -> open one -> Configs tab -> search for 'log.cleaner.min.compaction.lag.ms'
Edit-> set new value -> Save -> Confirm

I really saw twice when after setting new value there's displayed old one

Originally posted by @VladSenyuta in #271 (comment)