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: By rights this is wrong... an operation should only have one outcome. However for code cleanliness we may want to accept some fuzziness on exception paths. Still I think this should be investigated to see how hard it would be to fix. [comment](https://github.com/cljohnso/ehcache3/commit/85dba525bff089aa8b7cdf55bed2c0e384318ab0#commitcomment-8797484)