Move scripts used by travis jobs under travis folder because when mirroring all scripts folders are excluded

(cherry picked from commit 9a3588220b)

travis/scripts/cleanImages.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+set -x
+
+echo $imagesToBeDeleted
+echo "List all images:"
+docker images -a
+
+docker_images_list=$(docker images | grep $imagesToBeDeleted | awk '{print $3}' | uniq)
+if [ "$docker_images_list" == "" ]; then
+    echo "No docker images on the agent"
+else
+    echo "Clearing images: $docker_images_list"
+    if docker rmi -f $docker_images_list ; then
+        echo "Deleting images was successful."
+    else
+        echo "Deleting specified images failed, so falling back to delete ALL images on system."
+        docker rmi -f $(docker images -aq)
+    fi
+fi