Moving iptables rules to the relevant elements

This patch moves the iptables rules from elements/boot-stack to
an os-refresh-config/pre-configure.d directory within the element
that is relevant to the rule.
This patch relies on the add-rule script.

Change-Id: Idf0eca03f104829896b07693f1f22f31270c91c5
Fix exit status of haproxy install script

Don't return non-zero exit status if /etc/default/haproxy file doesn't exist,
image build fails then.

Change-Id: I64153a9f7869d1d7f7a4ce8f848884ba9fb83a37
Add nova-ironic element to replace nova-baremetal

Add new nova-ironic element which can be used in place of the existing
nova-baremetal element. These are not meant to be used together. This
patch also moves the Ironic ssh power key to /mnt/state.

NOTE: Nova "ironic" driver has not landed upstream yet, but this image
can be built with it ahead of time by setting the following:

  export DIB_REPOLOCATION_nova=https://review.openstack.org/openstack/nova
  export DIB_REPOREF_nova=refs/changes/28/51328

Change-Id: Ia8a61bf55f4337f40ee40b0fd381b2f776f67312
Merge "Add nova-ironic element to replace nova-baremetal"
Merge "Fix exit status of haproxy install script"
Merge "Moving iptables rules to the relevant elements"