Prior to 8.0.28 Tomcat required the key store and trust store (if any)
to be available directly on the filesystem, i.e. classpath: resources
would not work. Tomcat 8.0.28 removed this limitation.
This commit updates to Tomcat 8.0.28, updates the tests to verify
the new Tomcat capability and removes the obsolete documentation of
the restriction.
Closes gh-4048
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
