[rancid] frr/zebra more info

[Randy Bush]

currently, for frr systems,
  o i use `zebra` in the `router.db` definition
  o the rancid user on the target is ssh keyed (with command
    restriction)
  o the `/etc/passwd` entry for rancid has the shell defined as
    `/home/rancid/do-vtysh`
  o that script simply does `sudo /bin/vtysh`

and that works for the `show running config`

but i would also like to capture, archive, and diff
  o `/etc/network/interfaces` and
  o `/etc/nftables.conf`

do i hack the `/home/rancid/do-vtysh` script to simply `cat` them to
stdout?  i dread creating a new, or augmenting existing, rancid device
type.

randy