Explicitly use systemctl in logrotate

For some reason (Debian bug?) the default rsyslog-rotate script was not
properly rotating rsyslog logfiles. Instead, explicitly call systemctl
kill -s HUP for this, using a full path.

roles/base/templates/etc/logrotate.d/rsyslog.j2

@@ -16,6 +16,6 @@
 	delaycompress
 	sharedscripts
 	postrotate
-        /usr/lib/rsyslog/rsyslog-rotate &>/dev/null
+        /usr/bin/systemctl kill -s HUP rsyslog.service
 	endscript
 }