Issue #147 - Add non-bulk Ehcache unit tests

Adds unit tests for the following Ehcache methods:

* get
* put
* containsKey
* remove(key)
* clear
* iterator
* putIfAbsent
* remove(key, value)
* replace(key, value)
* replace(key, oldValue, newValue)
I would agree with your comment @cljohnso: do not test the value of the return, limit the assertion to the resilience strategy being called. This is really what we can assert without knowing what the strategy does.