Use vshard.router.map_callrw for map-reduce queries

[olegrok]

https://github.com/tarantool/vshard/commit/a394e3f4008a7436f011c81028dcaadc270eebf6

[DifferentialOrange]

Blocked by https://github.com/tarantool/vshard/issues/333

[olegrok]

Blocked by tarantool/vshard#333

But it's not so. You can use map_callrw only if mode is write and current logic for other cases. When https://github.com/tarantool/vshard/issues/333 will be solved you can replace "current" approach with map_callro/call_bro/...

[DifferentialOrange]

Blocked by tarantool/vshard#333

But it's not so. You can use map_callrw only if mode is write and current logic for other cases. When tarantool/vshard#333 will be solved you can replace "current" approach with map_callro/call_bro/...

I'm not sure it's worth to implement half-baked solution