util-mysql: remove mapistore dependecy

create_schema returns bool instead of mapistore_error.
Test adapted and moved to the proper test suite.

This change is needed to avoid dependecy of mapiproxy -> mapistore,
because util/mysql is used by both and mapistore already depends on
mapiproxy.
I always thought, until now, that talloc_free(NULL) will crash and destroy the world as we know it. We can remove this checks from several macros :ok_hand: