MB-11308: bumped node add timeout

On loaded VMs generating node certificate might take very long
time. Causing our existing timeouts to be hit.

Change-Id: I7a23cb7de6b65c2f3627e2cd2c8af8f7644b458e
Reviewed-on: http://review.couchbase.org/37882
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>