Fix KCM ccache per-type cursor

The KCM per-type cursor was too simplistic and did not obey the
conventions of the other ccache types.  Fix it to return a singleton
cursor when the default cache is a subsidiary and to return the
primary cache first.

For internal convenience, make_cache now accepts a context parameter
and creates a kcmio if necessary.

ticket: 8002 (new)
target_version: 1.13