tests: Check cgroup_add_controller return value in test_functions
tests: Check cgroup_add_controller return value in test_functions

Discovered by gcc 4.6 as "warning: variable ‘controller’ set but not used"

Signed-off-by: Jan Safranek <a7f4b96ffdd515ecef00f117294da18555749b0b@redhat.com>
Acked-by: Dhaval Giani <f48451d72a1ad74c777093928b661ad7099a85df@gmail.com>

rafalmiel/libcg,jrfastab/Linux-cgdcbxd,rafalmiel/libcg,jrfastab/Linux-cgdcbxd,jrfastab/Linux-cgdcbxd,rafalmiel/libcg,jrfastab/Linux-cgdcbxd,rafalmiel/libcg