Description of problem:
The "dnf needs-restarting -s" command fail when a mysql container is running in the same host and a "systemd-libs" update has been donwloaded by dnf-automatic.

The command seems to identify the MySQL container like a service.

Steps to Reproduce:
1. Deploy a MySQL container mapping the /var/lib/mysql to a volume.
2. dnf-automatic donwloads a new version of "systemd-libs" package.
3. Execute "dnf needs-restarting -s".

Actual results:
[root@xxxxxxx ~]# dnf needs-restarting -s
Traceback (most recent call last):
  File "/usr/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 201, in user_main
    errcode = main(args)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 67, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 106, in _main
    return cli_run(cli, base)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 122, in cli_run
    cli.run()
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 1055, in run
    return self.command.run()
  File "/usr/lib/python3.6/site-packages/dnf-plugins/needs_restarting.py", line 278, in run
    names = set([get_service_dbus(pid) for pid in sorted(stale_pids)])
  File "/usr/lib/python3.6/site-packages/dnf-plugins/needs_restarting.py", line 278, in <listcomp>
    names = set([get_service_dbus(pid) for pid in sorted(stale_pids)])
  File "/usr/lib/python3.6/site-packages/dnf-plugins/needs_restarting.py", line 142, in get_service_dbus
    systemd_manager_interface.GetUnitByPID(pid)
  File "/usr/lib64/python3.6/site-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib64/python3.6/site-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib64/python3.6/site-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.systemd1.NoUnitForPID: PID 1456 does not belong to any loaded unit.

Expected results:


Additional info:
"dnf needs-restarting -r" shows the following result:

Core libraries or services have been updated since boot-up:
  * systemd

Reboot is required to fully utilize these updates.
More information: https://access.redhat.com/solutions/27943