Pull images before running inside weaveexec container

Now we don't bundle the docker command inside weaveexec, we need to do
an explicit 'docker pull' to ensure the images are there.

Also set the weavedb tag to :latest to remove a warning from docker

weave

@@ -15,7 +15,7 @@ MIN_DOCKER_VERSION=1.10.0
 DOCKERHUB_USER=${DOCKERHUB_USER:-weaveworks}
 BASE_EXEC_IMAGE=$DOCKERHUB_USER/weaveexec
 EXEC_IMAGE=$BASE_EXEC_IMAGE:$IMAGE_VERSION
-WEAVEDB_IMAGE=$DOCKERHUB_USER/weavedb
+WEAVEDB_IMAGE=$DOCKERHUB_USER/weavedb:latest
 BASE_IMAGE=$DOCKERHUB_USER/weave
 IMAGE=$BASE_IMAGE:$IMAGE_VERSION
 PROXY_HOST=${PROXY_HOST:-$(echo "${DOCKER_HOST#tcp://}" | cut -s -d: -f1)}
@@ -219,6 +219,15 @@ case "$1" in
             fi
         fi
         ;;
+    launch)
+        # this is necessary because 'util_op run-container' doesn't do
+        # an implied pull like 'docker run' does
+        if [ -z "$IS_LOCAL" ] ; then
+            for img in $IMAGE $WEAVEDB_IMAGE ; do
+                docker inspect -f "_" $img >/dev/null 2>&1 || docker pull $img
+            done
+        fi
+        ;;
     setup)
         # call 'docker pull' outside weaveexec so we don't need a
         # docker binary inside