CRI: Add Buildah to ISO, for building OCI images

[afbjorklund]

After adding podman (#2757), also add buildah.

https://www.projectatomic.io/blog/2017/06/introducing-buildah/

This makes it possible to also build images...

Here is the buildah tutorial in minikube, slightly modified: (fedora -> alpine, java -> python)

                         _             _            
            _         _ ( )           ( )           
  ___ ___  (_)  ___  (_)| |/')  _   _ | |_      __  
/' _ ` _ `\| |/' _ `\| || , <  ( ) ( )| '_`\  /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )(  ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)

$ sudo -i
# buildah images
# buildah containers
CONTAINER ID  BUILDER  IMAGE ID     IMAGE NAME                       CONTAINER NAME
# container=$(buildah from alpine)
Getting image source signatures
Copying blob sha256:4fe2ade4980c2dda4fc95858ebb981489baec8c1e4bd282ab1c3560be8ff9bde
 2.10 MiB / 2.10 MiB [======================================================] 0s
Copying config sha256:196d12cf6ab19273823e700516e98eb1910b03b17840f9d5509f03858484d321
 1.48 KiB / 1.48 KiB [======================================================] 0s
Writing manifest to image destination
Storing signatures
# echo $container
alpine-working-container
# buildah run $container ash
container_linux.go:296: starting container process caused "process_linux.go:398: container init caused \"rootfs_linux.go:107: jailing process inside rootfs caused \\\"pivot_root invalid argument\\\"\""
error running container: error creating container for [/bin/ash]: : exit status 1
# buildah run --no-pivot $container ash
/ # apk add python
fetch http://dl-cdn.alpinelinux.org/alpine/v3.8/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.8/community/x86_64/APKINDEX.tar.gz
(1/10) Installing libbz2 (1.0.6-r6)
(2/10) Installing expat (2.2.5-r0)
(3/10) Installing libffi (3.2.1-r4)
(4/10) Installing gdbm (1.13-r1)
(5/10) Installing ncurses-terminfo-base (6.1_p20180818-r1)
(6/10) Installing ncurses-terminfo (6.1_p20180818-r1)
(7/10) Installing ncurses-libs (6.1_p20180818-r1)
(8/10) Installing readline (7.0.003-r0)
(9/10) Installing sqlite-libs (3.24.0-r0)
(10/10) Installing python2 (2.7.15-r1)
Executing busybox-1.28.4-r1.trigger
OK: 51 MiB in 23 packages
/ # exit
# buildah commit $container alpine-python
Getting image source signatures
Skipping fetch of repeat blob sha256:df64d3292fd6194b7865d7326af5255db6d81e9df29f48adde61a918fbd8c332
Copying blob sha256:79cf48ca68bf27b54c922e394bfdf3f7d93bc309e4ca3e9c647caa14e2f4eeb1
 12.37 MiB / 12.37 MiB [====================================================] 0s
Copying config sha256:433dc09a3d44ffbfc433dbd353944d15e2b41a561dcf6a410a8650521626def6
 702 B / 702 B [============================================================] 0s
Writing manifest to image destination
Storing signatures
433dc09a3d44ffbfc433dbd353944d15e2b41a561dcf6a410a8650521626def6
# buildah images
IMAGE ID             IMAGE NAME                                               CREATED AT             SIZE
196d12cf6ab1         docker.io/library/alpine:latest                          Sep 11, 2018 22:19     4.67 MB
433dc09a3d44         localhost/alpine-python:latest                           Oct 5, 2018 22:23      48.4 MB
# podman images
REPOSITORY                 TAG      IMAGE ID       CREATED          SIZE
localhost/alpine-python    latest   433dc09a3d44   45 seconds ago   48.4MB
docker.io/library/alpine   latest   196d12cf6ab1   3 weeks ago      4.67MB
# exit
logout

Opened containers/buildah#1071 for --no-pivot, same thing as $DOCKER_RAMDISK

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