Systemd units are a thin wrapper to the InstallUninstall template. Units
can be either system-wide (default) or user-session (by setting
$(unit).IsUser to non-empty value). The InstallDir is set to the
appropriate location for the unit type and is obtained by querying
pkg-config systemd module.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>