release: Build cloudware with multiple FS types

New ${CW}_FSLIST settings control the list of filesystem types with which
each cloudware image will be built; currently these are all set to "ufs",
i.e. no change from previous.

The cloudware images have their filesystem type as part of their file
name; for backwards compatibilty the ${VMFS} image is linked to the
previously used file name. This compatibility can be removed once all
the cloudware uploading/publishing code has been updated to use the new
image names (possibly more than one of them).

Reviewed by: gjb
Sponsored by: https://www.patreon.com/cperciva
Differential Revision: https://reviews.freebsd.org/D41341