Make gci mounter pre-fetch mounter image to reduce startup latency during runtime

Signed-off-by: Vishnu kannan <vishnuk@google.com>

cluster/gce/gci/mounter/mounter

@@ -24,13 +24,14 @@ ROOT_DIR=/home/kubernetes/bin
 RKT_BINARY=${ROOT_DIR}/rkt
 STAGE1_ACI=${ROOT_DIR}/stage1-fly.aci
 MOUNTER_ACI=${ROOT_DIR}/gci-mounter-${MOUNTER_VERSION}.aci
+MOUNTER_IMAGE=gcr.io/google_containers/gci-mounter:${MOUNTER_VERSION}
 
 function gc {
     # Attempt to garbage collect rkt pods with 5 retries.
     # Rkt pods end up creating new copies of mounts on the host. Hence it is ideal to clean them up right away.
     attempt=0
     until [ $attempt -ge 5 ]; do
-	${RKT_BINARY} gc --grace-period=0s && break
+	${RKT_BINARY} gc --grace-period=0s &> /dev/null && break
 	attempt=$[$attempt+1]
 	sleep 1
     done
@@ -39,12 +40,16 @@ function gc {
 # Garbage collect old rkt containers on exit
 trap gc EXIT
 
+if [[ ! $(${RKT_BINARY} image list | grep ${MOUNTER_IMAGE}) ]]; then
+        ${RKT_BINARY} fetch --insecure-options=image file://${MOUNTER_ACI}
+fi
+
 echo "Running mount using a rkt fly container"
 
 ${RKT_BINARY} run --stage1-path=${STAGE1_ACI} \
 	--insecure-options=image \
 	--volume=kubelet,kind=host,source=/var/lib/kubelet,readOnly=false,recursive=true \
 	--mount volume=kubelet,target=/var/lib/kubelet \
-	file://${MOUNTER_ACI} --user=${MOUNTER_USER} --exec /bin/mount -- "$@"
+	${MOUNTER_IMAGE} --user=${MOUNTER_USER} --exec /bin/mount -- "$@"
 
 echo "Successfully ran mount using a rkt fly container"

cluster/gce/gci/mounter/stage-upload.sh

@@ -1,5 +1,24 @@
 #!/bin/sh
 
+# Copyright 2016 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Due to the GCE custom metadata size limit, we split the entire script into two
+# files configure.sh and configure-helper.sh. The functionality of downloading
+# kubernetes configuration, manifests, docker images, and binary files are
+# put in configure.sh, which is uploaded via GCE custom metadata.
+
 set -o errexit
 set -o pipefail
 set -o nounset