[wp] makes -wp-gen tests more deterministic

src/plugins/wp/tests/test_config

src/plugins/wp/tests/wp_acsl/oracle/boolean.res.oracle

...ns/wp/tests/wp_acsl/oracle/chunk_typing_usable.res.oracle

src/plugins/wp/tests/wp_acsl/oracle/float_const.res.oracle

src/plugins/wp/tests/wp_acsl/oracle/inductive.res.oracle

src/plugins/wp/tests/wp_acsl/oracle/struct_fields.res.oracle

src/plugins/wp/tests/wp_acsl/oracle/sum_types.res.oracle

...plugins/wp/tests/wp_plugin/oracle/float_driver.res.oracle

src/plugins/wp/tests/wp_plugin/oracle/inductive.res.oracle