fix golint warnings/errors on pkg/system and pkg/stdcopy

Signed-off-by: Zhang Wei <zhangwei555@huawei.com>

system/filesys.go

@@ -6,6 +6,8 @@ import (
 	"os"
 )
 
+// MkdirAll creates a directory named path along with any necessary parents,
+// with permission specified by attribute perm for all dir created.
 func MkdirAll(path string, perm os.FileMode) error {
 	return os.MkdirAll(path, perm)
 }