Ensure that all Cypher tests close transactions reliably.

o Recent changes to database shutdown mean that we now wait for transactions
   to finish when shutting down. This mean that each of the many tests which did
   not close their transactions was hanging for 20 seconds before failing.
Fix tests that would be slowed by transaction leakage.

There are still about 18 tests that leak transactions, but those do so in a way
that it will not cause slow downs, I think.
Merge pull request #1490 from chrisvest/2.0-unclosed-txn-tests

Fix tests that would be slowed by transaction leakage.