Update the samples and integration tests to use Java 8. There's no
specific reason to keep them on Java 6 and it helps keep Eclipse happy
if we upgrade.
Switch the Tomcat 8 and Jetty 9 samples to Tomcat 7 and Jetty 8. Since
Tomcat 8 and Jetty 9 are now the default versions the previous samples
are no longer relevant, however, we do need integration tests to check
that we remain compatible with Tomcat 7 and Jetty 8.
See gh-1832
Phillip Webb
Spring Buildmaster
Andy Wilkinson