vshard: vshard.storage.cfg argument change

[TarantoolBot]

Related dev. issue(s): tarantool/vshard#426

Product: Tarantool, vshard
Since: 3.0 (vshard 0.1.25)
Root document:

• https://www.tarantool.io/en/doc/latest/how-to/vshard_quick/
• https://www.tarantool.io/en/doc/latest/reference/reference_rock/vshard/vshard_storage/#storage-api-cfg

SME: @ Serpentian

Details

vshard.storage.cfg(cfg, instance_id)

Configure the database and start sharding for the specified storage
instance. istance_id depends on identification_mode used in config.
If it's 'uuid_as_key', which is default, then UUID must be used.
Otherwise - instance_name.

Parameters:
cfg – a storage configuration
instance_id – UUID or name of the instance
Requested by @ Serpentian in tarantool/vshard@4c9cc51.