Test for fullsync's successful_exists status item
* After a fullsync, make sure that the numner of successful exists equals the number of partitions, since each partition should have one successful fullsync source process exit.
* We could extend this test to handle the parts of replication2 that have down nodes in the future.
* Added a utility function to get the number of partitions from a node, plus a function to get fullsync status items.
* Test passes with changes from branch cet-successful-exists-fix
Merge pull request #306 from basho/cet-successful-exists-test

Test for fullsync's successful_exists status item