Merge pull request #160 from cloudbuilders/mk_cachedir

create the uec cachedir if it doesn't exist. 
diff --git a/tools/get_uec_image.sh b/tools/get_uec_image.sh
index 3d62bba..cb59b9a 100755
--- a/tools/get_uec_image.sh
+++ b/tools/get_uec_image.sh
@@ -114,6 +114,7 @@
 # Get the UEC image
 UEC_NAME=$DIST_NAME-server-cloudimg-amd64
 if [ ! -e $CACHEDIR/$UEC_NAME-disk1.img ]; then
+    mkdir -p $CACHEDIR
     (cd $CACHEDIR && wget -N http://uec-images.ubuntu.com/$DIST_NAME/current/$UEC_NAME-disk1.img)
 fi