tests: Fix devlxd-container tests. (#275)

The `waitInstanceBooted` function was failing because systemctl inside
the container was sometimes reporting a degraded state after the force
stop. This doesn't matter for the purpose of this test. Now we just wait
for the instance to show some processes, then ensure that snapd is
running before we call `snap wait system seed.loaded`.

tests/devlxd-container

@@ -18,7 +18,7 @@ echo "==> Create storage pool using driver ${poolDriver}"
 lxc storage create "${poolName}" "${poolDriver}"
 
 echo "==> Create container and boot"
-lxc launch "${TEST_IMG:-ubuntu-minimal-daily:24.04}" c1 -s "${poolName}" -c security.nesting=true
+lxc launch "${TEST_IMG:-ubuntu:24.04}" c1 -s "${poolName}" -c security.nesting=true
 lxc info c1
 
 echo "==> Checking devlxd is working"
@@ -107,7 +107,7 @@ lxc monitor --type lifecycle --format json > monitor.json 2>&1 &
 monitorPID="${!}"
 
 # Launch an image we know is on the host.
-lxc exec c1 -- /snap/bin/lxc launch "${TEST_IMG:-ubuntu-minimal-daily:24.04}" c1c1
+lxc exec c1 -- /snap/bin/lxc launch "${TEST_IMG:-ubuntu:24.04}" c1c1
 lxc exec c1 -- /snap/bin/lxc info c1c1 | grep -F RUNNING
 
 kill -9 "${monitorPID}"