test/ovnpcli: Refactor to use GDBus++ D-Bus implementation

The openvpn3-linux ships with a netcfg-cli client, which is essentially
the same code as test/ovpncli/cli.cpp but it uses the
net.openvpn.v3.netcfg D-Bus service to create the virtual network
adapter and the related network and DNS configuration.  This is a useful
test client when only wanting to test the Network Configuration service
openvpn3-linux ships with.

As part of the refactoring of the D-Bus implementation in
openvpn3-linux, the supporting D-Bus setup needs to be adjusted to the
new D-Bus API.

It has been considered to support both types of APIs, but the legacy
D-Bus API is deprecated and will not be used any more after the release
of OpenVPN 3 Linux v22_dev.  Prior releases will depend on an older
OpenVPN 3 Core library version, which contains the old API.

Signed-off-by: David Sommerseth <[email protected]>

test/ovpncli/cli.cpp

@@ -1321,9 +1321,8 @@ int openvpn_client(int argc, char *argv[], const std::string *profile_content)
                     else
                     {
 #if defined(USE_NETCFG)
-                        DBus conn(G_BUS_TYPE_SYSTEM);
-                        conn.Connect();
-                        NetCfgTunBuilder<Client> client(conn.GetConnection());
+                        auto dbus_system = DBus::Connection::Create(DBus::BusType::SYSTEM);
+                        NetCfgTunBuilder<Client> client(dbus_system);
 #else
                         Client client;
 #endif