Add exec directory

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
make: etool -- Link with libct

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
make: Build protobuf data

We build only exec tool with protobuf for now.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
make: protobuf -- Link to exec and library itself

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>