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.
    #define TALLOC_FREE(ctx) do { talloc_free(ctx); ctx=NULL; } while(0)

both work, the macro version is in case you want to assure a crash if somebody use the freed pointer