zdtm: Force lib to be built before live targets

It's ugly but should work for now. Strictly speaking
I need to rework the complete make engine used in
zdtm.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Tested-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>