Test hooks `before/after` don't have examples nor clear API in the code

[Gerold103]

I tried to find which arguments they take and just couldn't. In the examples and in the code I couldn't find anything. Attempts to print the arguments resulted into messages like table 0x..... so I just gave up and needed to invent ugly stuff like this: https://github.com/tarantool/tarantool/blob/11e87877df9001a4972019328592d79d55d1bb01/test/replication-luatest/gh_5568_read_only_reason_test.lua#L12-L35

It would be logical for them to take their group as a first argument, but AFAIK it is not the group now. It is something else, I don't know what.