filter network candidate with new ifconfig output for install shim

new ifconfig output format is:
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet xxx.xxx.xxx.xxx  netmask 255.255.255.0  broadcast
	ether aa:bb:cc:dd:ee:ff  txqueuelen 1000  (Ethernet)

BUG=chrome-os-partner:23647
TEST=manually test on DUT w/o ethernet

Change-Id: I1af0cc4f627f329f197511dcd6f3c80ad576ed84
Reviewed-on: https://chromium-review.googlesource.com/179031
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Commit-Queue: Heng-ruey Hsu <henryhsu@chromium.org>
Tested-by: Heng-ruey Hsu <henryhsu@chromium.org>
1 file changed