crosperf: use mac address as machine id if VPD is not available.

For zgb machine, the dump_vpd_log --full --stdout does not return
serial number, in this case, we use mac address instead.

BUG=None
TEST=It get machine id for zgb

Change-Id: I1058dcd2a18638533c90a40d09adcc7a6bd8a660
Reviewed-on: https://gerrit-int.chromium.org/38900
Reviewed-by: Luis Lozano <llozano@chromium.org>
Tested-by: Yunlian Jiang <yunlian@google.com>
Commit-Queue: Yunlian Jiang <yunlian@google.com>
1 file changed