Checkmk Werk 14988: Agent controller: add support for systemd version 219

ID: 14988 Title: Agent controller: add support for systemd version 219 Component: agents Level: 1 Class: New feature Version: 2.2.0i1 This Werk brings support for systemd version 219 in case the agent controller is used. The limitation of the systemd version is due to the featureset required by the agent. In case the agent controller is used, the agent does not need the <tt>REMOTE_ADDR</tt> variable, in which case we can lower the required version from 220 to 219.