dict-client: Fix logging how much time was spent in other ioloops in slow lookup...

dict-client: Fix logging how much time was spent in other ioloops in slow lookup warnings.

The warning's idea is to show why the lookup could have been slow. We
differentiate between time spent in dict_wait() waiting only for the
dict result and time spent in other ioloops waiting for potentially other
things as well (and time spent waiting for locks during this time).

The previous code didn't work right when multiple ioloops were used, which
happened sometimes.

Also changed %u to %d just in case some calculation is wrong. It's nicer to
get a slightly negative value rather than a huge positive one.