Add tests for TransactionAwareCacheDecorator

This commit adds tests for TransactionAwareCacheDecorator. In
particular, the put/evict behaviour when the operation is invoked in
the course of Spring-managed transaction.
Merge pull request #462 from snicoll/cache-tx-tests

* cache-tx-tests:
  Add tests for TransactionAwareCacheDecorator
Fix cache decoration

Prior to this commit, a cache that is added on-the-fly is not properly
decorated by the provided CacheManager implementation that supports
it (EhCache and JCache).

This commits adds an extra getMissingCache method to
the AbstractCacheManager that can be extended to provide a cache that
may exist in the native cache manager but is not yet known by the
spring abstraction.

Issue: SPR-11518