Show current open file & connection limits when we hit then.

Make it easier to diagnose when we hit these limits - include the
current and maximum values in the log messages (if possible).

Change-Id: I75451d016cd38019831efe6429d31172c32d17d6
Reviewed-on: http://review.couchbase.org/38557
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>