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)
Chris Dennis: Hmm... this is right isn't it? No value in the store, means no remove, so the remove failed? [comment](https://github.com/cljohnso/ehcache3/commit/85dba525bff089aa8b7cdf55bed2c0e384318ab0#commitcomment-8797889)

Clifford Johnson: What are we tracking with RemoveOutcome.FAILURE -- infrastructure failures or "misses"? From the point of view of the cache user, the operation was successful ... the value is no longer in the cache. [comment](https://github.com/cljohnso/ehcache3/commit/85dba525bff089aa8b7cdf55bed2c0e384318ab0#commitcomment-8804198)