replace use of cirros 0.3.0 with 0.3.1

cirros 0.3.1 images have several significant improvements over 0.3.0, including:
 * newer kernel (3.2.0-25.40)
 * support for more filesystems (vfat, iso9660)
 * support for configdrive (config-drive-v2) as a datasource
 * acpi reboot/shutdown
 * curl with https support (previously there was no way to get https urls)

Change-Id: Idd7bef0cebb941f77d1cead9dc990fa0b03ff46b
diff --git a/lib/tempest b/lib/tempest
index e43f6d7..2ffd774 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -48,7 +48,7 @@
 BUILD_TIMEOUT=400
 
 
-BOTO_MATERIALS_PATH="$FILES/images/s3-materials/cirros-0.3.0"
+BOTO_MATERIALS_PATH="$FILES/images/s3-materials/cirros-0.3.1"
 
 # Entry Points
 # ------------
@@ -273,8 +273,8 @@
 
 # init_tempest() - Initialize ec2 images
 function init_tempest() {
-    local base_image_name=cirros-0.3.0-x86_64
-    # /opt/stack/devstack/files/images/cirros-0.3.0-x86_64-uec
+    local base_image_name=cirros-0.3.1-x86_64
+    # /opt/stack/devstack/files/images/cirros-0.3.1-x86_64-uec
     local image_dir="$FILES/images/${base_image_name}-uec"
     local kernel="$image_dir/${base_image_name}-vmlinuz"
     local ramdisk="$image_dir/${base_image_name}-initrd"