vold: allow execute cp and rm

Used in system/vold/MoveTask.cpp

Addresses:
avc: denied { execute } for name="toolbox" dev="mmcblk0p29" ino=359 scontext=u:r:vold:s0 tcontext=u:object_r:toolbox_exec:s0 tclass=file permissive=1
avc: denied { read open } for path="/system/bin/toolbox" dev="mmcblk0p29" ino=359 scontext=u:r:vold:s0 tcontext=u:object_r:toolbox_exec:s0 tclass=file permissive=1
avc: denied { execute_no_trans } for path="/system/bin/toolbox" dev="mmcblk0p29" ino=359 scontext=u:r:vold:s0 tcontext=u:object_r:toolbox_exec:s0 tclass=file permissive=1

Change-Id: I2eb6288aaed510ae5be0f3605088ace6b865ef83