Shares the /health endpoint request mapping between security config
and MVC dispatcher. Generalizes so that instead of a marker
interface (AnonymouslyAccessibleMvcEndpoint), an MvcEndpoint
signals that it wants to control its own access rules by adding
a Principal to the @RequestMapping method parameters (more @MVC).
Fixes gh-2015 slightly differently
Makes them a lot more readable IMO, and also enables @Autowiring
from the context into the test case (sweeet). I added @DirtiesContext
to all of them as well to be on the safe side, but possbly that can be
optimized in some way as well.
