Comment 17 for bug 1711735

He means simply removing "trusty + armhf" for the "ros" and/or
"gazebo" images, I believe (not for the "ubuntu" image).

The harm this causes is that "apt-get update" fails, which causes the
whole "docker build" to fail.

Here's an example from ppc64el:

W: Failed to fetch
http://security.ubuntu.com/ubuntu/dists/trusty-security/main/binary-ppc64el/Packages
 404 Not Found [IP: 91.189.88.152 80]

W: Failed to fetch
http://security.ubuntu.com/ubuntu/dists/trusty-security/restricted/binary-ppc64el/Packages
 404 Not Found [IP: 91.189.88.152 80]

W: Failed to fetch
http://security.ubuntu.com/ubuntu/dists/trusty-security/universe/binary-ppc64el/Packages
 404 Not Found [IP: 91.189.88.152 80]

W: Failed to fetch
http://security.ubuntu.com/ubuntu/dists/trusty-security/multiverse/binary-ppc64el/Packages
 404 Not Found [IP: 91.189.88.152 80]

E: Some index files failed to download. They have been ignored, or old
ones used instead.