Remove an excess cp of disk images.

save_image is used to copy kernel and ramdisks out of the image, which
we will sometimes want to keep the source, and sometimes not. However
for the main image itself, the temp copy is never kept, so use mv
  rather than cp and avoid the excess IO.

Change-Id: I5a9f0d69ffee3e6b872a8927537ac17f02f5aa4d

bin/disk-image-create

@@ -187,5 +187,7 @@ unmount_image
 if [ "$IS_RAMDISK" == "0" ]; then
   compress_and_save_image $IMAGE_NAME.$IMAGE_TYPE
 else
-  remove_image
+  # This is a ramdisk build, we have already extracted the kernel and ramdisk
+  # by this point.
+  rm $TMP_IMAGE_PATH
 fi

lib/common-functions

@@ -40,6 +40,14 @@ function mk_build_dir () {
   export TMP_HOOKS_PATH=$TMP_BUILD_DIR/hooks
 }
 
+function finish_image () {
+    mv $TMP_IMAGE_PATH $1
+    cleanup_dirs
+    # All done!
+    trap EXIT
+    echo "Image file $1 created..."
+}
+
 function save_image () {
     # TODO: this really should rename the old file
     if [ -f  $1 ] ; then

lib/img-functions

@@ -106,13 +106,7 @@ function compress_and_save_image () {
     rm $TMP_IMAGE_PATH
 
     TMP_IMAGE_PATH=$1-new
-    save_image $1
-    remove_image
-}
-
-function remove_image () {
-  echo "Removing $TMP_IMAGE_PATH"
-  rm $TMP_IMAGE_PATH
+    finish_image $1
 }
 
 function do_extra_package_install () {