Add image building config file for Fedora and py3

Here's an image building configuration file that can be used to build
overcloud full images on Fedora 28.

Change-Id: I43e3dbcfeab4f5237e79f42bad39e52bed9aef0e
Related-Blueprint: python3-support

image-yaml/overcloud-images-fedora.yaml

@@ -0,0 +1,22 @@
+disk_images:
+  -
+    imagename: overcloud-full
+    type: qcow2
+    distro: fedora
+    elements:
+      - selinux-permissive
+    environment:
+      FS_TYPE: xfs
+    packages:
+      - yum-plugin-priorities
+    options:
+      - "--mkfs-options '-s size=4096'"
+  -
+    imagename: ironic-python-agent
+    type: qcow2
+    distro: fedora
+    elements:
+      - selinux-permissive
+    packages:
+      - yum-plugin-priorities
+

image-yaml/overcloud-images-python3.yaml

@@ -0,0 +1,61 @@
+disk_images:
+  -
+    imagename: overcloud-full
+    type: qcow2
+    elements:
+      - baremetal
+      - dhcp-all-interfaces
+      - openvswitch
+      - overcloud-agent
+      - overcloud-base
+      - overcloud-controller
+      - overcloud-compute
+      - overcloud-ceph-storage
+      - puppet-modules
+      - stable-interface-names
+      - grub2
+      - element-manifest
+      - dynamic-login
+      - iptables
+      - enable-packages-install
+      - override-pip-and-virtualenv
+      - dracut-regenerate
+      - remove-machine-id
+      - remove-resolvconf
+      - openssh
+      - disable-nouveau
+    packages:
+      - python-psutil
+      - python-debtcollector
+      - plotnetcfg
+      - sos
+      - ntp
+      - device-mapper-multipath
+      - openstack-heat-agents
+      - os-net-config
+      - jq
+      - dbus-python
+    options:
+      - "--min-tmpfs=7"
+    environment:
+      DIB_PYTHON_VERSION: '3'
+  -
+    imagename: ironic-python-agent
+    # This is bogus, but there's no initrd type in diskimage-builder
+    type: qcow2
+    # So we just override the extension instead
+    imageext: initramfs
+    elements:
+      - ironic-agent
+      - ironic-agent-multipath
+      - dynamic-login
+      - element-manifest
+      - network-gateway
+      - enable-packages-install
+      - override-pip-and-virtualenv
+    packages:
+      - python-hardware-detect
+    options:
+      - "--min-tmpfs=7"
+    environment:
+      DIB_PYTHON_VERSION: '3'