By default, podman points PIDFile in generated unit file to non-existent
location. As a result, the unit file, generated by podman, is broken:
an attempt to start this unit without prior modification results in a crash,
because systemd can not find the pidfile of service's main process.
Fix the value of "PIDFile" and add a system test for this case.
Signed-off-by: Danila Kiver <danila.kiver@mail.ru>