Inefficient usage of cache due to "ADD plugins-archive /"

[Radosław Piliszek]

A few images (-base) use:
ADD plugins-archive /
to deliver plugins to the build.
However, the way kolla builds that tarball invalidates the cache every time even with no changes to plugins. This is inefficient.

See:
https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#leverage-build-cache
and:
https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#add-or-copy

[Roman Krček (r-krcek)]

This seems to occur because git leaves some files in the .git folder that contain the time when the repository was cloned, among other things. Thus always invalidating cache. To fix this problem, different approach to including plugins into the image would have to be taken.