Rework @TestPropertySource changes introduced in commit d251b513
to restore compatibility with Spring Boot 1.1

- Only add the `server.port` property when no @IntegrationTest
  annotation is found.
- Always add a default `spring.jmx.enabled=false` property.
- Restore the SpringApplicationContextLoader.getEnvironmentProperties
  protected method.
- Remove the @IntegrationTest.properties attribute.

See gh-1697