Revert "Bump cirros version to 0.6.1"

This reverts commit 91efe177b170c3874989affc73842dc4ffbe062d.

Reason for revert: it broke tempest-slow job https://9afe3d390e4175b60a80-89b1085289883615a17bd93ef47f6ca9.ssl.cf5.rackcdn.com/871018/13/gate/tempest-slow-py3/d139ae1/testr_results.html

Change-Id: Ib74e51a780d3e8101f4147db9d24eebea4980fb1
diff --git a/doc/source/guides/nova.rst b/doc/source/guides/nova.rst
index d0fb274..5b42797 100644
--- a/doc/source/guides/nova.rst
+++ b/doc/source/guides/nova.rst
@@ -122,7 +122,7 @@
 .. code-block:: shell
 
   $ openstack --os-compute-api-version 2.37 server create --flavor cirros256 \
-      --image cirros-0.6.1-x86_64-disk --nic none --wait test-server
+      --image cirros-0.3.5-x86_64-disk --nic none --wait test-server
 
 .. note:: ``--os-compute-api-version`` greater than or equal to 2.37 is
           required to use ``--nic=none``.