box: add option to disable Lua FFI for read operations

Box read operations (select, min, max, random, pairs) may call a Lua
function via Lua C API if space upgrade (EE feature) is in progress.
This is forbidden if the original function was called via FFI:

https://github.com/tarantool/luajit/commit/4f4fd9ebeb10d53c8e67f45170938f052818e64e

Let's add helper functions to disable FFI for box read operations.
We will use them in EE code.

NO_DOC=internal
NO_TEST=internal
NO_CHANGELOG=internal