WIP: GEOMESA-202 Consolidate unit tests so they share one AccumuloDataStore

Pushed up for comments. Waiting for other PR's to get merged in,
since there will definitely be conflicts.

Found areas where Mock Accumulo instances could be shared between tests,
merged some of the separate Iterator tests into the MultiIteratorTest,
added @jnh5y's indexSchemaFormat suggestion to most test DataStore params,
and cleaned up some specs2 code style. All changes should save about
1 min 30 secs in complete build time.
If testing the IndexIterator is suitably folded into the STIITest, we can delete this class.  

Otherwise, I imagine this is running the STIITest again.