Add a couple of negative unit tests

This patch series adds a couple of negative unit tests in order to make sure we fail in case of invalid conf options. * [PATCH 1/2] conf/test: add a negative unit test for invalid pci Above patch makes sure we fail if invalid pci specific global feature is specified. * [PATCH 2/2] conf/test: add a negative test for invalid Above patch makes sure we fail if invalid config arrtinute for acpi-bridge-hotplug is specified.