CBQE-0: catch unhandled exception for viewverification task

Change-Id: I2a59c4981a28f1d477c0e2ebaf919c79b38ed356
Reviewed-on: http://review.couchbase.org/26103
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>