ci: untangle getting test images

This simplifies and optimizes getting container images used for tests.

Currently, we have three different ways of getting images:

1. (for hello-world) the image is in this repo under tests/integration/testdata.

2. (for busybox) download it from github (the repo that is used for
   preparing official Docker image) using curl.

3. (for debian) download from Docker hub, using skopeo and umoci.

To further complicate things, we have to do this downloading in multiple
scenarios (at least 4): locally, in github CI, from Dockefile, inside a
Vagrant VM. For each scenario, we have to install skopeo and umoci, and
those two are not yet universally available for all the distros that we
use.

Yet another complication is those images are used for tests/integration
(bats-driven tests) as well as for libcontainer/integration (go tests).
The tests in libcontainer/integration rely on busybox being available
from /busybox, and the bats tests just download the images to a
temporary location during every run.

It is also hard to support CI for other architectures, because all
the machinery for preparing images is so complicated.

This commit is an attempt to simplify and optimize getting images,
mostly by getting rid of skopeo and umoci dependencies, but also
by moving the download logic into one small shell script, which
is used from all the places.

Benefits:

 - images (if not present) are only downloaded once;
 - same images are used for both kind of tests (go and bats);
 - same images are used for local and inside-docker tests
   (because source directory is mounted into container);
 - the download logic is located within 1 simple shell script.

[v2: fix eval; more doc to get-images; print URL if curl failed]
[v3: use "slim" debian, twice as small]
[v4: fix not using $image in setup_bundle]
[v5: don't remove TESTDATA from helpers.bash]
[v6: add i386 support]

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Dockerfile

@@ -1,14 +1,11 @@
 ARG GO_VERSION=1.15
 ARG BATS_VERSION=v1.2.1
-ARG UMOCI_VERSION=v0.4.6
 
 FROM golang:${GO_VERSION}-buster
 ARG DEBIAN_FRONTEND=noninteractive
 
 RUN echo 'deb https://download.opensuse.org/repositories/devel:/tools:/criu/Debian_10/ /' > /etc/apt/sources.list.d/criu.list \
     && wget -nv https://download.opensuse.org/repositories/devel:/tools:/criu/Debian_10/Release.key -O- | apt-key add - \
-    && echo 'deb http://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/Debian_10/ /' > /etc/apt/sources.list.d/skopeo.list \
-    && wget -nv https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable/Debian_10/Release.key -O- | apt-key add - \
     && dpkg --add-architecture armel \
     && dpkg --add-architecture armhf \
     && dpkg --add-architecture arm64 \
@@ -35,7 +32,6 @@ RUN echo 'deb https://download.opensuse.org/repositories/devel:/tools:/criu/Debi
         libseccomp2 \
         pkg-config \
         python-minimal \
-        skopeo \
         sudo \
         uidmap \
     && apt-get clean \
@@ -56,21 +52,4 @@ RUN cd /tmp \
     && ./install.sh /usr/local \
     && rm -rf /tmp/bats-core
 
-# install umoci
-ARG UMOCI_VERSION
-RUN curl -o /usr/local/bin/umoci -fsSL https://github.com/opencontainers/umoci/releases/download/${UMOCI_VERSION}/umoci.amd64 \
-    && chmod +x /usr/local/bin/umoci
-
 WORKDIR /go/src/github.com/opencontainers/runc
-
-# setup a playground for us to spawn containers in
-COPY tests/integration/multi-arch.bash tests/integration/
-ENV ROOTFS /busybox
-RUN mkdir -p "${ROOTFS}"
-RUN . tests/integration/multi-arch.bash \
-    && curl -fsSL `get_busybox` | tar xfJC - "${ROOTFS}"
-
-ENV DEBIAN_ROOTFS /debian
-RUN mkdir -p "${DEBIAN_ROOTFS}"
-RUN . tests/integration/multi-arch.bash \
-    && get_and_extract_debian "$DEBIAN_ROOTFS"