Offer only what this machine can deliver

The installer knew one distribution: Debian, with docker, on a new enough
release. Everything else it would have offered and then failed at.

Three facts now decide what the matrix offers, and each is read from the
machine rather than assumed:

- The container runtime. Docker where the machine has one, podman on the Red
  Hat family, which ships no docker at all. Both go through the same compose
  plugin: compose speaks the Docker API and podman serves it, so there is one
  compose file and one deployment path, not two. Telling a Fedora operator to
  add Docker's own repository to a machine that already has a container
  runtime would have been the wrong trade.

- glibc. The server binary is downloaded, not built here, and it is linked
  against 2.39. Rocky 9 (2.34), Debian 12 and Ubuntu 22.04 cannot run it, so
  the host shape is refused there with the version found and the container
  shape named as the answer -- rather than installing a file that cannot
  start.

- The operating system itself. This compiles for macOS and Windows because Go
  compiles anything, and on either it would read no os-release, find no
  systemd, and describe a machine that does not exist. It now says what it is
  and exits.

Two bugs the other distributions found, both of which Debian could not have:

- The survey reported the first thing in the way and stopped, so on Fedora it
  asked to start podman.socket, and then -- having done it -- asked for the
  compose plugin. Needs are named now, not described, and reported together.

- apply used the survey taken before dependencies were installed, so on a
  machine that had no runtime at all it installed podman and then reached for
  docker. It re-surveys after resolving, and stops if containers still are
  not usable.

The lab takes DISTRO now: debian13, debian12, ubuntu2404, fedora, rocky9,
arch, each with its own disk and ssh port so several can be up at once. The
cases no longer say "docker" either. install-local passes on Debian 13,
Fedora 43 and Rocky 9 -- 20 checks each, ending with a sign-in to the webmail
the installer put there.

e2e/vm/up.sh

@@ -7,10 +7,17 @@
 # The installer writes units, creates users, takes 25 and 443 and can install
 # a web server. None of that belongs on a workstation, and none of it can be
 # proved in a container either -- systemd, users and ports are the thing under
-# test. So: a Debian cloud image in qemu, seeded with cloud-init, with a copy
-# of the disk kept the moment it is up. Every run starts from that copy, so a
-# run can break the machine as thoroughly as it likes.
+# test. So: a distribution's own cloud image in qemu, seeded with cloud-init,
+# with a copy of the disk kept the moment it is up. Every run starts from that
+# copy, so a run can break the machine as thoroughly as it likes.
 #
+# DISTRO picks which: debian13 (the default), debian12, ubuntu2404, fedora,
+# rocky9 or arch. They are not interchangeable, which is the point -- podman
+# rather than docker on the Red Hat family, firewalld on by default there, and
+# a glibc on Rocky 9 older than the server binary needs. Each has its own
+# directory and ssh port, so several can be up at once.
+#
+#   DISTRO=fedora e2e/vm/up.sh
 #   e2e/vm/up.sh       build it and keep a clean copy (idempotent)
 #   e2e/vm/reset.sh    back to the clean copy, a few seconds
 #   e2e/vm/run.sh      build the installer, copy it in, run a case inside
@@ -24,13 +31,16 @@
 # Needs: qemu-system-x86_64, /dev/kvm, xorriso, ssh, curl.
 set -euo pipefail
 
-LAB="${LAB:-$HOME/.cache/inbuxa-lab}"
+. "$(dirname "$0")/lib.sh"
+
+DISTRO="${DISTRO:-debian13}"
+LAB="${LAB:-$HOME/.cache/inbuxa-lab/$DISTRO}"
 MEM="${MEM:-4096}"
 VCPUS="${VCPUS:-2}"
 DISK_GB="${DISK_GB:-20}"
-SSH_PORT="${SSH_PORT:-2222}"
-BASE_URL="https://cloud.debian.org/images/cloud/trixie/latest/debian-13-genericcloud-amd64.qcow2"
-BASE="$LAB/debian-13-base.qcow2"
+SSH_PORT="${SSH_PORT:-$(distro_port "$DISTRO")}"
+BASE_URL="${BASE_URL:-$(distro_image "$DISTRO")}"
+BASE="$LAB/base.qcow2"
 DISK="$LAB/lab.qcow2"
 CLEAN="$LAB/lab-clean.qcow2"
 SEED="$LAB/seed.iso"
@@ -39,8 +49,8 @@ PIDFILE="$LAB/qemu.pid"
 KEY="${KEY:-$HOME/.ssh/id_ed25519.pub}"
 
 say() { echo "==> $*"; }
-. "$(dirname "$0")/lib.sh"
 
+[ -n "$BASE_URL" ] || { echo "unknown distribution '$DISTRO' (debian13, debian12, ubuntu2404, fedora, rocky9, arch)" >&2; exit 1; }
 [ -r "$KEY" ] || { echo "no public key at $KEY (set KEY=)" >&2; exit 1; }
 [ -w /dev/kvm ] || { echo "no writable /dev/kvm -- is this user in the kvm group?" >&2; exit 1; }