[async] Delay crashes in async body till async:wait is called.
[async] Delay crashes in async body till async:wait is called.

That way async:wait will produce more useful diagnostics, not just a
simple noproc error.

Change-Id: I9a8360e5e6b4601a7148fd7f4cede54dea59250e
Reviewed-on: http://review.couchbase.org/84703
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Tested-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server