Update of-watchdog to 0.8.1

Signed-off-by: Rogier <rogier@blijblijblij.com>

Move to Ruby 2.6.3 and Debian

This change updates Ruby and makes native packages such as
nokogiri very simple to build and consume.

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

Update to multi-arch image

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

Initial version of Ruby template ported to of-watchdog

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>