Use the latest 0.3.5 version of CirrOS

This new version of CirrOS is built on top of 0.3 branch, so wrt
version 0.3.4 it includes only two commits:

- Cherry-pick of the fix for https://launchpad.net/bugs/1564948
- One extra fix to make the above working on 0.3

Cherry-picked commit is http://bazaar.launchpad.net/~cirros-dev/cirros/trunk/revision/366

A Tempest test for hard reboot in some cases hits the case where
host key are empty. This triggers bugs/1564948, i.e. the ssh
daemon does not start at all, and the Tempest test fails with
"connection refused", which is misleading.

The new version of CirrOS solves this problem as it ensure host
keys are generated if missing, and the sshd deamon started.

I tested the scenario of missing host keys in Iea74c63925be17a1df894c1a2c23f5ba2793e0c6
using a private build of what then became 0.3.5.

Change-Id: I5c154ec25555e768954538fc22b4f5d5975b2deb

stackrc

@@ -614,7 +614,7 @@ esac
 #IMAGE_URLS="http://smoser.brickies.net/ubuntu/ttylinux-uec/ttylinux-uec-amd64-11.2_2.6.35-15_1.tar.gz" # old ttylinux-uec image
 #IMAGE_URLS="http://download.cirros-cloud.net/${CIRROS_VERSION}/cirros-${CIRROS_VERSION}-${CIRROS_ARCH}-disk.img" # cirros full disk image
 
-CIRROS_VERSION=${CIRROS_VERSION:-"0.3.4"}
+CIRROS_VERSION=${CIRROS_VERSION:-"0.3.5"}
 CIRROS_ARCH=${CIRROS_ARCH:-"x86_64"}
 
 # Set default image based on ``VIRT_DRIVER`` and ``LIBVIRT_TYPE``, either of