mirror: in CI, do not run apt-get update on the host

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

examples/dr-config-apt-local-mirror.yaml

@@ -0,0 +1,7 @@
+apt_mirrors_known:
+  - url: http://mymirror.local/repository/Apt/ubuntu/
+    strategy: failure
+  - pattern: 'https?://[a-z]{2,}\.archive\.ubuntu\.com/ubuntu/?'
+    strategy: success
+  - url: http://archive.ubuntu.com/ubuntu
+    strategy: failure

scripts/runtests.sh

@@ -215,6 +215,7 @@ LANG=C.UTF-8 timeout --foreground 60 \
     --machine-config examples/existing-partitions.json \
     --bootloader bios \
     --autoinstall examples/autoinstall.yaml \
+    --dry-run-config examples/dr-config-apt-local-mirror.yaml \
     --kernel-cmdline autoinstall \
     --source-catalog examples/install-sources.yaml
 validate