Deprecate the deploy-ironic element

Completed in Kilo the blueprint ipa-as-default-ramdisk [1] ported all
the Ironic drivers in tree to be able to use the IPA ramdisk for the
deployment.

Now in Liberty the blueprint deprecate-bash-ramdisk is deprecating the
bash ramdisk created using the "deploy-ironic" element in DIB.

This patch is printing a deprecation message when the user uses the
"deploy-ironic" element and as well updating the README file to indicate
that it has been deprecated.

[1] https://blueprints.launchpad.net/ironic/+spec/ipa-as-default-ramdisk
[2] https://blueprints.launchpad.net/ironic/+spec/deprecate-bash-ramdisk

Related-Blueprint: deprecate-bash-ramdisk
Change-Id: I8057f52104225326f45eb3ae6065cd02a27f5ef2

elements/deploy-ironic/README.rst

@@ -3,3 +3,7 @@ deploy-ironic
 =============
 A ramdisk that will expose the machine primary disk over iSCSI and reboot
 once Ironic signals it is finished.
+
+.. warning::
+   This element is deprecated.  Please use the ironic-agent element
+   instead.

elements/deploy-ironic/root.d/00-ironic-deploy-deprecated

@@ -0,0 +1,21 @@
+#!/bin/bash
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+if [ ${DIB_DEBUG_TRACE:-1} -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+echo "WARNING: The deploy-ironic element is deprecated. Please use the ironic-agent element instead." 1>&2