MB-10127 Drop messages in error_logger if mailbox is to large.

Change-Id: I85fd89a9e65ff66a96cd5134e0c101bc1b0f358c
Reviewed-on: http://review.couchbase.org/33335
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>