Checkmk Werk 12680: Linux-Agent: Place systemd units at /usr/lib

ID: 12680 Title: Linux-Agent: Place systemd units at /usr/lib Component: Checks & agents Level: 1 Class: Bug fix Version: 2.1.0i1 Previously, the RPM/DEB owned systemd units were placed at /etc/systemd/system. Now, they are placed at /usr/lib/systemd/system/. A sysadmin can now drop specific overrides into /etc/systemd/system/ to customize the units. With this change users who want to customize specific systemd behaviour can follow the officially documented systemd workflow to change only what they want, resulting in a cleaner workflow. This merges Github PR #240. Thanks go to jcpunk for contribution!