Build discovery ramdisk using dracut

Removes the busybox install in the discovery ramdisk element (it
should be handled by the ramdisk element anyway) and adds the
appropriate dib option to use dracut.

elements/discovery-ironic/binary-deps.d/discovery-ironic

@@ -1,4 +1,3 @@
-busybox
 curl
 dmidecode
 fdisk

elements/discovery-ironic/install.d/52-discovery-ironic-install-busybox

@@ -1,6 +0,0 @@
-#!/bin/bash
-
-set -eu
-set -o pipefail
-
-install-packages busybox

scripts/instack-build-images

@@ -152,6 +152,7 @@ function discovery-ramdisk {
         ramdisk-image-create \
             -a $NODE_ARCH \
             -o $DISCOVERY_NAME \
+            --ramdisk-element dracut-ramdisk \
             $NODE_DIST $DISCOVERY_IMAGE_ELEMENT \
             $DIB_COMMON_ELEMENTS \
             2>&1 | tee dib-discovery.log