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've used this name to keep it like `OPENCHANGE_RETVAL_*` macros

The side effect is also present in all `*_RETVAL_*` macros across all codebase. I don't see that as an issue meanwhile everyone knows what the macro is doing, which we all know. :bowtie: