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: In the presence of failure this should be calling the resilience strategy. We can discuss what "should" happen here... but it relates partly to the reworking of the new concurrent methods. [comment]  (https://github.com/cljohnso/ehcache3/commit/9096c8936a58ed373ad978fc6aeb0225b7b34422#commitcomment-8798447)

Clifford Johnson: The resilience strategy is being called (confirmed in line 173 below). It could be argued that the return value shouldn't be tested here (since the resilience strategy is the code providing the answer and would, more rightly, be tested in a resilience strategy test than here ... but then, we need tests for the default strategy -- and I've not really covered that. [comment](https://github.com/cljohnso/ehcache3/commit/9096c8936a58ed373ad978fc6aeb0225b7b34422#commitcomment-8803747)