[ale] Reimplement disk sink without using disk_log.

Rotation is currently not supported. And sync can still block callers.

Change-Id: Ifa894debf30650a7daf95cdd4e963bf69b2f7b49
Reviewed-on: http://review.couchbase.org/37746
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
[ale] Add size based rotation support to disk sink.

Change-Id: Ia8458611926ec5bf4b35ae002ef1549153fb6674
Reviewed-on: http://review.couchbase.org/37747
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>