Simplistic conversion of old log files to new format.

We just rename the files and don't bother to compress them. Eventually
these old files will get rotated.

Change-Id: I68e1b126972b6505a5ba8312efc451084d1bca8c
Reviewed-on: http://review.couchbase.org/37943
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>