tests: Don't use D-Bus custom names when mocking systemd's Manager

Because org.freedesktop.systemd1 busname is often used even as session
busname we had to improvise in systemd tests and we used custom name
cz.cesnet.systemd1 along with custom object paths and interfaces
when mocking systemd's D-Bus behaviour.
This is not necessary.
There is no need to create custom paths and interfaces, we can use the
standard ones. We only have to use another bus name.

Change-Id: Ied5dbfe9ad2fec2bd30787d5d6916bf5a5924fd9
diff --git a/tests/dbus-helpers/dbus_systemd_server.cpp b/tests/dbus-helpers/dbus_systemd_server.cpp
index 2d461d3..dcb96c9 100644
--- a/tests/dbus-helpers/dbus_systemd_server.cpp
+++ b/tests/dbus-helpers/dbus_systemd_server.cpp
@@ -5,9 +5,9 @@
 using namespace std::literals;
 
 namespace {
-static const std::string interfaceUnit = "cz.cesnet.systemd1.Unit";
-static const std::string interfaceManager = "cz.cesnet.systemd1.Manager";
-static const std::string objectPathManager = "/cz/cesnet/systemd1";
+static const std::string interfaceUnit = "org.freedesktop.systemd1.Unit";
+static const std::string interfaceManager = "org.freedesktop.systemd1.Manager";
+static const std::string objectPathManager = "/org/freedesktop/systemd1";
 }
 
 /** @brief Create a dbus server on the connection */