Fixed exception propagation test.

Test was broken due to mocha intercepting uncaught
exceptions, even when using domains.  Corrected test
to override mocha for this particular test.

Change-Id: I8fb58a26bded88878c66d88ee174b48faece1408
Reviewed-on: http://review.couchbase.org/36557
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>
Tested-by: Brett Lawson <brett19@gmail.com>