Switch to minideb as base image

[hiddeco]

In versions of Alpine 3.4 and later, a name resolution issue was
introduced and causes problems with certain Kubernetes setups. The
issue appears to be incosistent and difficult to reproduce (but has been
detected on CentOS and NixOS setups). Moving away from Alpine seems the
best option for now.

Fixes #2051, addresses #1980, #1148

[2opremio]

@hiddeco Can you post the before and after image differences here?

[squaremo]

Looks like bitnami/minideb:stretch is rebuilt daily, and there are no versioned releases :-/ Technically we can trace any given image back to its constituent layers, but this still makes me a bit nervous. (Mind you the same was probably true of the alpine image)

[hiddeco]

weaveworks/flux                               2015-base-minideb-7179d16c                    1ff0f07d6866        3 minutes ago       282MB
weaveworks/flux                               master-416e8420                               d3f2bc77ebc6       28 seconds ago      169MB

weaveworks/helm-operator                      2015-base-minideb-7179d16c                    ca706b8ae43d        53 seconds ago       291MB
weaveworks/helm-operator                      master-416e8420                               821749f0eeae        46 seconds ago       169MB

The Helm operator image size is weird, it installs less packages but ends up being bigger?

[stefanprodan]

@hiddeco an alternative to bitnami would be debian:stable-slim this is used by GitHub. The official image has image scanning enabled see https://hub.docker.com/_/debian?tab=tags

[stefanprodan]

Another thing to consider, using bitnami/minideb image we lose ARM support. I would go with debian:stable-slim since it's multi-arch (x86, arm, arm64).

[2opremio]

I had forgotten about ARM support, plus debian/slim has date-tags which help tracking down what's being run.

I think we should give it a try, thanks @stefanprodan