Fix burnin ImportExport CreateInstance opcode

This patch adds the two attributes file_storage_dir and file_driver
to the CreateInstance opcode in the ImportExport method, since
otherwise it will fail with the file storage patches.

Reviewed-by: iustinp

tools/burnin

@@ -305,7 +305,9 @@ class Burner(object):
                                         start=True,
                                         ip_check=True,
                                         wait_for_sync=True,
-                                        mac="auto")
+                                        mac="auto",
+                                        file_storage_dir=None,
+                                        file_driver=None)
       erem_op = opcodes.OpRemoveExport(instance_name=instance)
 
       Log("- Export instance %s to node %s" % (instance, enode))