Add nodes_wanted() variant that takes config as a parameter.

Change-Id: I3085f46fb077e85e395e10ea66b3d640d4f1a81f
Reviewed-on: http://review.couchbase.org/35290
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Remove leftover per node keys upon switching to 3.0 compat mode.

Change-Id: Ic1e447f263513d096c455a6e7d6f7c9ae8871471
Reviewed-on: http://review.couchbase.org/35291
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>