Add example of creating per-node os-net-config mappings

Adds an example of proving a mapping file for all nodes, then
extracting the data for each node based on a lookup of the mac address.

Some assumptions are made (e.g the hard-coded reference to eth0), but
it should be easily modified to suit specific environments.

Usage via an enviroment file will look like:

resource_registry:
  OS::TripleO::NodeUserData: os-net-config-mappings.yaml
parameter_defaults:
  NetConfigDataLookup:
    host1:
      nic1: "00:c8:7c:e6:f0:2e"
    host2:
      nic1: "00:18:7d:99:0c:b6"

Note this version requires liberty heat in the undercloud due to the
use of a new str_replace feature to serialize the json parameter.

Change-Id: I7da9c9d8805e676a383e888a7d77f05d3432ab12

firstboot/os-net-config-mappings.yaml

@@ -0,0 +1,65 @@
+heat_template_version: 2015-10-15
+
+description: >
+  Configure os-net-config mappings for specific nodes
+  Your environment file needs to look like:
+    parameter_defaults:
+      NetConfigDataLookup:
+        node1:
+          nic1: "00:c8:7c:e6:f0:2e"
+        node2:
+          nic1: "00:18:7d:99:0c:b6"
+  This will result in the first nodeN entry where a mac matches a
+  local device being written as a mapping file for os-net-config in
+  /etc/os-net-config/mapping.yaml
+
+parameters:
+  # Note this requires a liberty heat or newer in the undercloud due to
+  # the 2015-10-15 (which is required to enable str_replace serializing
+  # the json parameter to json, another approch with a string parameter
+  # will be required for older heat versions)
+  NetConfigDataLookup:
+    type: json
+    default: {}
+    description: per-node configuration map
+
+resources:
+  userdata:
+    type: OS::Heat::MultipartMime
+    properties:
+      parts:
+      - config: {get_resource: OsNetConfigMappings}
+
+  OsNetConfigMappings:
+    type: OS::Heat::SoftwareConfig
+    properties:
+      group: ungrouped
+      config:
+        str_replace:
+          template: |
+            #!/bin/sh
+            eth_addr=$(/sbin/ifconfig eth0 | grep ether | awk '{print $2}')
+            mkdir -p /etc/os-net-config
+
+            # Create an os-net-config mapping file, note this defaults to
+            # /etc/os-net-config/mapping.yaml, so we use that name despite
+            # rendering the result as json
+            echo '$node_lookup' | python -c "
+            import json
+            import sys
+            import yaml
+            input = sys.stdin.readline() or '{}'
+            data = json.loads(input)
+            for node in data:
+              if '${eth_addr}' in data[node].values():
+                interface_mapping = {'interface_mapping': data[node]}
+                with open('/etc/os-net-config/mapping.yaml', 'w') as f:
+                  yaml.safe_dump(interface_mapping, f, default_flow_style=False)
+                break
+            "
+          params:
+            $node_lookup: {get_param: NetConfigDataLookup}
+
+outputs:
+  OS::stack_id:
+    value: {get_resource: userdata}