If SYSTEMDSYSTEMUNITDIR is defined, the systemd units are automatically
installed. Therefore consequently also install the required config files
in that case.
Example:
$ make install SYSTEMDSYSTEMUNITDIR=/usr/lib/systemd/system/
Reviewed-by: Benjamin Block <bblock@linux.vnet.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
