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: I53cd7d24759454a680aa85bd0f9132f3b111f25f
diff --git a/tempest/api/compute/images/test_images_negative.py b/tempest/api/compute/images/test_images_negative.py
index 63ba650..e91944f 100644
--- a/tempest/api/compute/images/test_images_negative.py
+++ b/tempest/api/compute/images/test_images_negative.py
@@ -67,7 +67,7 @@
         resp = {}
         resp['status'] = None
         self.assertRaises(lib_exc.NotFound, self.create_image_from_server,
-                          '!@$%^&*()', name=name, meta=meta)
+                          '!@$^&*()', name=name, meta=meta)
 
     @test.attr(type=['negative'])
     @test.idempotent_id('ec176029-73dc-4037-8d72-2e4ff60cf538')