wicket's errors should be better when trying to read sensitive data from ssh without a pseudo-tty

wicket uses rpassword to read sensitive data during RSS configuration (e.g., the recovery silo password, bgp auth keys). When ssh'ing over wicket, one has to remember to use ssh -t wicket@IP command...; without the -t, ssh doesn't allocate a pseudo-terminal, and we get a pretty arcane error back:

$ ssh wicket@IP setup set-bgp-auth-key "bgpkey"
current BGP authentication keys (0/1 set):
  • bgpkey: unset

setting 1 key to use TCP-MD5 authentication
Error: failed to read MD5 authentication key

Caused by:
    No such device or address (os error 6)

We should do better here; ideally we could at least suggest trying ssh -t if we think that could be the problem (which it almost always is, in practice!).

Start at wicket's RSS configuration path where rpassword reads sensitive data, especially the BGP authentication key flow. Reproduce the setup command over SSH without a pseudo-terminal, then verify that the resulting error clearly suggests using ssh -t when no pseudo-terminal is available.