tests(e2e): filter out releases with no VM images (#1035)

Rather than have the e2e tests failing constantly until an image becomes
available, we can be smarter about it and dynamically exclude the
codename until the Azure CLI reports at least one existing image for it.

Of course, this doesn't directly map to the existence of a customized
image built by our "E2E - Build image templates" workflow -- but it
gives a clue as to when it becomes possible to build such an image.

-----------

This came as a result of the TICS job failing because it couldn't find a
passing E2E job from which to download the PAM coverage, and with us
enabling Oracular tests none of the jobs would actually be passing
anymore (until a Oracular VM template becomes available). This is a
band-aid for that, and hopefully for future occurrences as well.

I've tested this locally (oracular is excluded):
https://github.com/GabrielNagy/adsys/actions/runs/9611677172

.github/workflows/e2e-tests.yaml

@@ -32,7 +32,10 @@ jobs:
       - name: Install needed binaries
         run: |
           sudo apt-get update
-          sudo DEBIAN_FRONTEND=noninteractive apt-get install -y distro-info
+          sudo DEBIAN_FRONTEND=noninteractive apt-get install -y distro-info jq
+      - uses: azure/login@v2
+        with:
+          creds: ${{ secrets.AZURE_CREDENTIALS }}
       - name: Build matrix
         id: set-supported-releases
         run: |
@@ -49,6 +52,12 @@ jobs:
                   continue
               fi
 
+              # Filter out releases with no corresponding Azure images
+              images="$(az vm image list --publisher Canonical --offer 0001-com-ubuntu-minimal-${r} --all)"
+              if [ "$(jq '(. | length) == 0' <<<${images})" = "true"  ]; then
+                  continue
+              fi
+
               if [ -n "${releases}" ]; then
                   releases="${releases}, "
               fi

e2e/scripts/provision.sh

@@ -25,6 +25,9 @@ if [[ ! "$(lsmod)" =~ cifs ]]; then
     echo "cifs" >> /etc/modules
 fi
 
+echo "Disabling unattended-upgrades to avoid unexpected dpkg frontend locks..."
+systemctl disable --now unattended-upgrades
+
 echo "Updating DNS resolver to use AD DNS..."
 echo "DNS=10.1.0.4" >> /etc/systemd/resolved.conf
 systemctl restart systemd-resolved