ci deb: tweak downgrade test case

Now, no need to unmask td-agent because transitional
td-agent package was installed before.

Signed-off-by: Kentaro Hayashi <[email protected]>

Author: kenhys

fluent-package/apt/systemd-test/downgrade-to-v4.sh

@@ -20,13 +20,13 @@ sudo apt install -V -y \
     /host/${distribution}/pool/${code_name}/${channel}/*/*/fluent-package_*_${architecture}.deb \
     /host/${distribution}/pool/${code_name}/${channel}/*/*/td-agent_*_all.deb
 
-# td-agent.service is already masked (link to /dev/null), and remove td-agent.service alias not to conflict with v4
-sudo systemctl unmask td-agent
+sudo systemctl is-active fluentd
+sudo systemctl is-active td-agent
 
 # Even though removing fluent-package, log and .conf are kept. dpkg reports "rc fluent-package" and "rc td-agent" status.
 sudo apt remove -y fluent-package td-agent
 
-# fluentd.service is already masked (link to /dev/null), then remove it.
+# fluentd.service is already masked (link to nonexistent /lib/systemd/system/fluentd.service), then remove it.
 sudo systemctl unmask fluentd
 
 # Drop symbolic links and recreate real directory.