libct/cg/sd: escape dbus address value

D-Bus specification [1] requires that the values in server address need
to be escaped in a special way, and other clients perform the needed
escaping (e.g. systemd [2] does that, as well as recent godbus [3]).

More to say, it is important to perform such escaping, since if dbus
sees a character that should have been escaped but it's not, it returns
an error [4].

Fix tryDiscoverDbusSessionBusAddress to use dbus.EscapeBusAddressValue
function, recently added to godbus [3].

[1] https://dbus.freedesktop.org/doc/dbus-specification.html#addresses
[2] https://github.com/systemd/systemd/blob/5efbd0bf897a990ebe43d7dc69141d87c404ac9a/src/libsystemd/sd-bus/bus-internal.c#L294-L318
[3] godbus/dbus#302
[4] https://gitlab.freedesktop.org/dbus/dbus/-/blob/37b76d13738e782fe2eb12abdd0179745c0b3f81/dbus/dbus-address.c#L330

Signed-off-by: Kir Kolyshkin <[email protected]>

libcontainer/cgroups/systemd/user.go

@@ -87,7 +87,7 @@ func DetectUserDbusSessionBusAddress() (string, error) {
 	if xdr := os.Getenv("XDG_RUNTIME_DIR"); xdr != "" {
 		busPath := filepath.Join(xdr, "bus")
 		if _, err := os.Stat(busPath); err == nil {
-			busAddress := "unix:path=" + busPath
+			busAddress := "unix:path=" + dbus.EscapeBusAddressValue(busPath)
 			return busAddress, nil
 		}
 	}