Add flag validation diskspace and set false(skip) step by default (#909)

* flag validation diskspace

* display Available disk space

* update image.CI

* add image.CI flag

* update env RUN_VALIDATION_FLAG

images/linux/scripts/installers/validate-disk-space.sh

@@ -8,6 +8,12 @@ availableSpaceMB=$(df / -hm | sed 1d | awk '{ print $4}')
 minimumFreeSpaceMB=17800
 
 echo "Available disk space: $availableSpaceMB MB"
+
+if [ $RUN_VALIDATION != "true" ]; then
+    echo "Skipping validation disk space..."
+    exit 0
+fi
+
 if [ $availableSpaceMB -le $minimumFreeSpaceMB ]; then
     echo "Not enough disk space on the image (minimum available space: $minimumFreeSpaceMB MB)"
     exit 1