test-install: Wait for network in the lxc container.

Ubuntu 20.04 "focal" comes up to runlevel 5 several seconds before it
is able to successfully resolve hosts, causing `prepare-base` to fail
while fetching from the apt repositories.

Add an additional check to verify that outbound networking is running
before returning from `lxc-wait`.

tools/test-install/lxc-wait

@@ -27,16 +27,36 @@ if [ "$EUID" -ne 0 ]; then
 fi
 
 # We poll.
-for _ in {1..60}; do
-    echo "lxc-wait: $CONTAINER_NAME: polling for boot..." >&2
-    runlevel="$(lxc-attach --clear-env -n "$CONTAINER_NAME" -- runlevel 2>/dev/null)" \
-        || { sleep 1; continue; }
-    if [ "$runlevel" != "${0%[0-9]}" ]; then
-        echo "lxc-wait: $CONTAINER_NAME: booted!" >&2
-        exit 0
-    fi
-    sleep 1
-done
+poll_runlevel() {
+    for _ in {1..60}; do
+        echo "lxc-wait: $CONTAINER_NAME: polling for boot..." >&2
+        runlevel="$(lxc-attach --clear-env -n "$CONTAINER_NAME" -- runlevel 2>/dev/null)" \
+            || { sleep 1; continue; }
+        if [ "$runlevel" != "${0%[0-9]}" ]; then
+            echo "lxc-wait: $CONTAINER_NAME: booted!" >&2
+            poll_network
+        fi
+        sleep 1
+    done
+    echo "error: timeout waiting for container to boot" >&2
+    exit 1
+}
+
+
+poll_network() {
+    for _ in {1..60}; do
+        echo "lxc-wait: $CONTAINER_NAME: polling for network..." >&2
+        # New hosts don't have `host` or `nslookup`
+        lxc-attach --clear-env -n "$CONTAINER_NAME" -- \
+                   ping -q -c 1 archive.ubuntu.com 2>/dev/null >/dev/null \
+            || { sleep 1; continue; }
+        echo "lxc-wait: $CONTAINER_NAME: network is up!" >&2
+        exit 0
+    done
+    echo "error: timeout waiting for container to get network" >&2
+    exit 1
+}
+
+
+poll_runlevel
 
-echo "error: timeout waiting for container to boot" >&2
-exit 1