wdctl; read from /sys if necessary

wdctl; read from /sys if necessary

The device can be inaccessible for non-root user or busy (already used
by another process). In this case it seems better to read information
from /sys.

Note that /sys does not provide struct watchdog_info.options, so we
cannot print list of supported watchdog features.

Addresses: https://github.com/karelzak/util-linux/issues/804
Signed-off-by: Karel Zak <kzak@redhat.com>