info: Add --is tls, --can structured-reply

While these are per-connection rather than per-export settings, it is
still useful to have a quick-and-silent command-line query rather than
having to parse full info output.

While touching info-can.sh, strengthen it to insist that an
unsupported feature is reported with status 2, rather than any
non-zero status.

Message-Id: <20221011215213.214246-3-eblake@redhat.com>
Acked-by: Richard W.M. Jones <rjones@redhat.com>