Use random query for essential test

Use the random query generator in the essential test. This will cause
1-3 terms to be queried with varying cardinality in an attempt to give a
more thorough test.
Change essential test to transition from 2 to 4 nodes

Change the transition to go from 2 to 4 nodes (rather than 3 to 4) so
that overlapped replicas will exist. This makes sure the overlapped
replicas can exist and the query results are still correct.
Merge pull request #283 from basho/rz/better-test

Better essential test
Merge remote-tracking branch 'origin/develop' into refactor/rz/port-kv-140-updates