MB-5844 move ns_log and isasl.pw files from the data directory

to avoid conflicts with bucket names
the files are moved one level up to the /data/<node> dir

Change-Id: I08a9d0c3f0c8a567e85a437ac4c8f16fb506f6f3
Reviewed-on: http://review.couchbase.org/27903
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>