Instance ID was corrected

Regarding with RFC3986 percent character '%' must be followed by the two
hexadecimal digits. In other cases WSGI server can reject such  request.

Change-Id: I284091afd4e1e28c9c66972d15eeb105b9ba9217
diff --git a/tempest/api/compute/images/test_images_negative.py b/tempest/api/compute/images/test_images_negative.py
index 6555b64..54a82e9 100644
--- a/tempest/api/compute/images/test_images_negative.py
+++ b/tempest/api/compute/images/test_images_negative.py
@@ -108,7 +108,7 @@
     def test_delete_image_with_invalid_image_id(self):
         # An image should not be deleted with invalid image id
         self.assertRaises(lib_exc.NotFound, self.client.delete_image,
-                          '!@$%^&*()')
+                          '!@$^&*()')
 
     @test.attr(type=['negative'])
     @test.idempotent_id('137aef61-39f7-44a1-8ddf-0adf82511701')