Rework the new testing support so that @SpringApplicationTest can be
used for standard integration tests, web integration tests with a
mock Servlet environment and web integration tests with an embedded
servlet container. This means that it a replacement for 1.3's
@IntegrationTest and @WebIntegrationTest and allows all
SpringApplication testing to be configured using a common annotation.
The old @IntegrationTest and @WebIntegrationTest along with their
supporting classes have been reinstated to their previous form (while
remaining deprecated). This should ensure that they continue to work
in 1.4 exactly as they did in 1.3 giving users a smooth path to
@SpringApplicationTest.
See gh-5477
