Alpine runtime container

[AriPaaWun]

Use Alpine (openjdk:8-jdk-alpine) as build platform
Use Alpine (openjdk:8-jre-alpine) as runtime

Had to explicitly ignore warnings when building nginx-clojure.

I have no idea if --no-cache has any effect on update&upgrade.

I'm released this as 1.12.2-0.4.5-2.1, 1.12.2-0.4.5-alpine and latest. It can be a breaking change to many things, but as far as I know, at the moment we are the only one using this. Version 1.12.2-0.4.5 will stay as it is until the heat death of the universe. Docker Hub

[pvalkone]

I have no idea if --no-cache has any effect on update&upgrade.

The --no-cache option is exactly what we want, since we don't want to leave the package cache behind after we're finished installing packages.

As of Alpine Linux 3.3 there exists a new --no-cache option for apk. It allows users to install packages with an index that is updated and used on-the-fly and not cached locally [...] This avoids the need to use --update and remove /var/cache/apk/* when done installing packages.

https://github.com/gliderlabs/docker-alpine/blob/master/docs/usage.md#disabling-cache

[pvalkone]

Add the --no-cache option to the update, upgrade and add commands.
See: https://github.com/gliderlabs/docker-alpine/blob/master/docs/usage.md#disabling-cache