baremetal: VirtualPowerDriver uses mac addresses in bm_interfaces

After the change I6653829364b0a641442d45e766493180d6f2a880,
bm_nodes.prov_mac_address is no longer set. However VPD still
uses it. This patch changes VPD to use bm_interfaces.address
instead of bm_nodes.prov_mac_address.

Fixes bug 1168574.

Change-Id: I2bab869b282958ee9fd0e4776928e56351018324
Merge "baremetal: VirtualPowerDriver uses mac addresses in bm_interfaces"