Move the ensure_nbd function call.

Move the ensure_nbd function call from the disk-image-create to the
disk-image-get-kernel. The image creation process does not use qemu-nbd
anymore.

Change-Id: I8ff2ad54f322a9e33d52408fa4e253a7b45900c7

bin/disk-image-create

@@ -92,9 +92,6 @@ IMAGE_ELEMENT=$($SCRIPT_HOME/element-info --expand-dependencies $IMAGE_ELEMENT)
 echo "Building elements: $IMAGE_ELEMENT"
 echo "If prompted for sudo, install sudoers.d/img-build-sudoers into /etc/sudoers.d and restart the build."
 
-# TODO: make into an element.
-ensure_nbd
-
 mk_build_dir
 create_base
 run_d extra-data

bin/disk-image-get-kernel

@@ -68,6 +68,8 @@ source $_LIB/img-functions
 
 echo "Extracting kernel + ramdisk from $IMAGE_FILE and writing them to $OUT_DIR"
 
+ensure_nbd
+
 # sets WORK_DIR
 mount_qcow_image $IMAGE_FILE