[apt-retry] - Added logic to retry apt update

When there is failure to fetch any of the apt urls, it skips and
continues. Due to which apt install fails in next step.
So added retry if apt fetch fails before proceeding to apt install.

Change-Id: I658024481b1be98d280cb1c9c4c2fb733a0d5697

promenade/templates/include/up.sh

@@ -82,15 +82,16 @@ set -x
 
 end=$(($(date +%s) + APT_INSTALL_TIMEOUT))
 while true; do
-    if ! apt-get update; then
+    if ! apt-get update 2>&1 | grep -q '^W: Failed to fetch'; then
+        break
+    else
         now=$(date +%s)
         if [[ ${now} -gt ${end} ]]; then
-            log Failed to update apt-cache.
+            log "Failed to update apt-cache."
             exit 1
         fi
+        log "re-try apt-get update..."
         sleep 10
-    else
-        break
     fi
 done