Fix leak in DurabilityUnitTest::testDuplicateCommands

We should use the two-arg createConnection() which provides a scoped
'HandleWrap' object.

Change-Id: I83417944db0dd3d506214ef924618643119ad6f1
Reviewed-on: http://review.couchbase.org/43026
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>