MB-100: feed binaries to ns_log for some memory savings

I've seen some avalance of crashes that we log into ns_log,
overloading ns_log quite easily. Part of that was some uneeded error
logging to standard output which is fixed in another commit. But I
also saw that ns_log doesn't store it's messages very
efficiently. I.e. it's using stringish-iolists (mostly lists of chars
with occasional atoms). Clearly, converting it to more efficient
iolist is a win.

Change-Id: Iabdd2aff36c66ed56400120fa775e723b4b1810b
Reviewed-on: http://review.couchbase.org/25574
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>