deb: fix update current behavior about updating from v4 (#711)

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

fluent-package/apt/systemd-test/update-from-v4.sh

@@ -44,7 +44,10 @@ esac
 
 # Test: service status
 systemctl status --no-pager fluentd
-(! systemctl status --no-pager td-agent)
+# BUG: v4 service restart logic will not launched usually because the
+# existence check of td-agent.service will always fail.
+# As a result, old service is still alive here.
+systemctl status --no-pager td-agent
 
 # Test: restoring td-agent service alias
 sudo systemctl stop fluentd