This is sort of continuation of the previous patch. The partition key in
the registry is now table_id, not string, and is better called "owner",
not "location". This patch is s/location/owner/ over specific places
that include field name in the schema, argument names in registry
maintenance classes and tests accessing the selected row fields by name.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>