Update default cirros version

Cirros has a new release 0.4.0, which fixes a couple of issues.

Change-Id: I419348f1784600e3989c8e86a99c04b24f3610c4

Author: jharbott

stackrc

@@ -685,7 +685,7 @@ ENABLE_UBUNTU_CLOUD_ARCHIVE=$(trueorfalse True ENABLE_UBUNTU_CLOUD_ARCHIVE)
 #IMAGE_URLS="http://smoser.brickies.net/ubuntu/ttylinux-uec/ttylinux-uec-amd64-11.2_2.6.35-15_1.tar.gz" # old ttylinux-uec image
 #IMAGE_URLS="http://download.cirros-cloud.net/${CIRROS_VERSION}/cirros-${CIRROS_VERSION}-${CIRROS_ARCH}-disk.img" # cirros full disk image
 
-CIRROS_VERSION=${CIRROS_VERSION:-"0.3.6"}
+CIRROS_VERSION=${CIRROS_VERSION:-"0.4.0"}
 CIRROS_ARCH=${CIRROS_ARCH:-"x86_64"}
 
 # Set default image based on ``VIRT_DRIVER`` and ``LIBVIRT_TYPE``, either of