box/schema.func: add option to not copy dynamic libraries

Added option box.cfg.module_copy_on_load (true by default) which specifies how the dynamic libraries are loaded.

If set to true, the libraries are copied into a temporary directory before dlopen is called. This is needed to work around the caching built in to dlopen and reloading dynamic modules via box.schema.func.reload.

If set to false, the libraries are loaded as is, which allows the tools like perf to gather detailed statistics.