No longer hard coding to a specifc network interface name.

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