Use "ip" instead of "ifconfig" to get MAC address

"ifconfig" get different formats of output under different systems,
like CentOS and Fedora, but "ip" can provide uniform format, so we
use "ip" instead of "ifconfig" to get MAC address.

Change-Id: If7559ea96c96ed2f33ddb00737ee0f53f7de4990
Closes-Bug: 1381416
Merge "Use "ip" instead of "ifconfig" to get MAC address"