cgroup_test: Add a test for devices subsystem

1.Confirm if file cannot be created in desired device if
  this device was set to access deny by cgroup
2.Confirm if file can be created in desired device if
  this device was set to access allow by cgroup

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Merge pull request #25 from liyangfnst/device_access

cgroup_test: Add a test for devices subsystem