config: introduce vshard named identification

Vshard now supports names instead of UUIDs in configuration. Let's
use them and finally drop generating UUIDs in config.

From now on we can recover instances without explicitly passing
UUIDs to configuration.

NO_DOC=<not released yet>
NO_CHANGELOG=<not released yet>

Co-authored-by: Mergen Imeev <imeevma@tarantool.org>