Add hypervisors ancillary files list

These lists will be used to declare some of the files not necessarily
needed on all nodes. The files selected are files without which the
various hypervisors can still work, but that when they are present
should be synchronized across the cluster (or node group).

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>