JSCBC-77: Fixed bug with expiry times on get.

Fixed typo where lock time was used instead of expiry time.
Additionally added unit tests for testing expiry times.

Change-Id: I0b463e5036410d610557e399bbcfa280a1af783f
Reviewed-on: http://review.couchbase.org/30140
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Brett Lawson <brett19@gmail.com>