There are two path parsers. One of them accepts keyspace and table names
and the other one doesn't. The latter is then supposed to parse the
ks.cf pair from path and put it on the descriptor. This patch makes this
method return ks.cf so that later it will be possible to remove these
strings from the desctiptor itself.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>