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.
The macro has a side effect that could surprise. consider:

   MAPISTORE_RETVAL_ERR(do_something(a,b), mem_ctx);

`do_something()` is going to get called twice