No longer hard coding to a specifc network interface name.

Instead of using a specific network interface name, thi fix
fetch all ethernet mac addresses. Then uses this list of
mac addresses to do a check if any entries in the list
match any of the values in NetConfigDataLookup for a node.
If there is a match, the /etc/os-net-config/mapping.yaml
file for the node will be written.

This fix removes the hard coded interface name 'eth0' used
to get a mac address as identifyer for the specific node
before. Using a hard coded interface name such as 'eth0'
would have failed on most hardware because of "consistent
network device names".

    Fix Bug: #1642551

Change-Id: I6c1d1b4d70b916bc5d9049469df8221f8ab2eb95

firstboot/os-net-config-mappings.yaml

@@ -38,7 +38,7 @@ resources:
         str_replace:
           template: |
             #!/bin/sh
-            eth_addr=$(/sbin/ifconfig eth0 | grep ether | awk '{print $2}')
+            eth_addr=$(cat /sys/class/net/*/address | tr '\n' ',')
             mkdir -p /etc/os-net-config
 
             # Create an os-net-config mapping file, note this defaults to
@@ -51,7 +51,7 @@ resources:
             input = sys.stdin.readline() or '{}'
             data = json.loads(input)
             for node in data:
-              if '${eth_addr}' in data[node].values():
+              if any(x in '$eth_addr'.split(',') for x 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)