Fix seedlist to not return duplicate json keys

Previously, we used `lists:ukeymerge` which only works if the entries in the
list are kept in a sorted order, but they weren't. Since we now have maps
available in Erlang, use those instead of proplists which would avoid the
sorting issue.

While at it, make sure to test the `_up` and `_uuids` "misc" handler endpoints
and modernize the seedlist test suite as well.
5 files changed