Inconsistent return types in storage local_call for older Tarantool versions

[kamenkremen]

With older Tarantool versions, when a called function is not registered in the schema, it is called via netbox; otherwise, it is executed by a func.call. This creates inconsistency between return types because netbox converts return type from cdata to a lua type, whereas a direct func.call does not.

[Serpentian]

Reincarnation of the tarantool/tarantool#4513, but specific to vshard and only to the functions, defined in the box.func.