configure Ethernet management interface MAC addresses

Reviewed By: vidya, dustin

At boot time set each Ethernet management interface MAC address based
on the output of the 'onie-sysinfo -e' command.

Testing Done:

Exercised the code changes on both PowerPC and x86_64 platforms.  In
both cases verified that the eth0 MAC address matched the output of
'onie-sysinfo -e'.