to avoid the test failure

 7) Test driver "xen"  ... 2016-03-31 12:53:26.950+0000: 22430: debug : virDriverLoadModule:54 : Module load xen
 2016-03-31 12:53:26.950+0000: 22430: error : virDriverLoadModule:73 : failed to load module /build/libvirt-1.3.3~rc1/debian/build/src/.libs/libvirt_driver_xen.so /build/libvirt-1.3.3~rc1/debian/build/src/.libs/libvirt_driver_xen.so: undefined symbol: xlu_cfg_destroy
FAILED

(cherry picked from commit 12b239a9)