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.
Merge pull request #101 from openchange/jgarcia/fix-broken-mapiproxy-symbols

util-mysql: remove mapistore dependecy