box: fetch UUIDs from cfg instead of func args

There were a few places where instance and replicaset UUIDs from
box.cfg where passed as arguments in box.cc functions. It was fine
although sometimes could cause struggling like "where along the
callstack replicaset UUID is created when it was nil in cfg".

But soon the situation will get more complicated. There will be up
to 3 new arguments - cluster, replicaset, and instance names.

Passing all these identifiers as parameters would be cumbersome.
The patch makes the UUIDs fetched from the config by the functions
which need them. The same will be done with the names where they
are relevant.

Needed for #5029

NO_DOC=refactoring
NO_CHANGELOG=refactoring
NO_TEST=already covered