Multiple errors: readiness and shutdown checks

The existing readiness check (org.keycloak.testsuite.arquillian.containers.KeycloakQuarkusServerDeployableContainer#waitForReadiness) has proven to be unreliable on Quarkus, in part because REST endpoints are brought up before the actual startup has completed. This leads to multiple test errors.

A prototype based on MicroProfile Health has shown much better results. As soon as MP Health support lands in Keycloak, the testsuite should be ported to MP Health too. Additionally, container.waitFor() should be added to the stop() method to avoid false positives in waitForReadiness().