Add support for arm32v7 and arm64v8 with Gazebo v9

[ruffsl]

Fixes: #173

See available package listings:

• http://packages.osrfoundation.org/gazebo/ubuntu-stable/dists/bionic/main/binary-amd64/Packages
• http://packages.osrfoundation.org/gazebo/ubuntu-stable/dists/bionic/main/binary-armhf/Packages
• http://packages.osrfoundation.org/gazebo/ubuntu-stable/dists/bionic/main/binary-arm64/Packages
• http://packages.osrfoundation.org/gazebo/debian-stable/dists/stretch/main/binary-amd64/Packages
• http://packages.osrfoundation.org/gazebo/debian-stable/dists/stretch/main/binary-armhf/Packages
• http://packages.osrfoundation.org/gazebo/debian-stable/dists/stretch/main/binary-arm64/Packages

[ruffsl]

I figured I'd add images for debian to match what we support for our ROS images, and updated the template file to reflect this. @j-rivero , let me know if this addition seems sound.

[lag-linaro]

LGTM

[ruffsl]

Merging and letting CI generate a PR to bump the version.

[odidev]

Hi Guys,

Gazebo at Docker-Hub still supports amd64 architecture only.
It seems it needs a PR at https://github.com/docker-library/official-images/blob/master/library/gazebo to update the new list of architectures.

Regards,

[ruffsl]

@odidev , docker-library/official-images#5096 is already staged.

[odidev]

Thanks, @ruffsl for a quick update.