Given that Spring Boot uses java config accross the board, a new `value`
attribute is now aliased to the existing `classes` attribute such that
one could write the following:
@SpringApplicationConfiguration(MyConfig.class)
public class MyTest {}
Closes gh-3635
JUnit tests can now be @SpringApplicationConfiguration
and @IntegrationTest without any explicit imports. Also
makes @RunWith(SpringJUnit4ClassRunner) optional.
Fixes gh-969