MB-8872 add basic auth to all issued _view_merge and _spatial_merge requests

with user = ns_server and password = erlang:get_cookie()

Change-Id: I9456f3f0d2f9dee199a78748e7e11ed0e111ffee
Reviewed-on: http://review.couchbase.org/43375
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>