Fix tomcat maven repo location and use spring.io

Fix the maven repo used for tomcat 8 release candidates and update
spring repos from springsource.org to spring.io.
Expand var-args before passing to KeyGenerator

Update `CacheAspectSupport` to expand any var-arg parameters before
calling `KeyGenerator` implementations. Prior to this commit var-args
would be passed to `KeyGenerator` implementations as a nested array,
often causing the same key to be generated regardless of the arguments.

Issue: SPR-10870