Netperf Runner: Restart netserver on failure

CL:292944 revealed that in some situations netserv exits while
running repeated netperf tests.  This CL restarts netserv when
this condititon is detected.

BUG=chromium:490408
TEST=Run network_WiFi_Perf.ht20 test from a drone
TEST=(These failures never reproed from my desk)

Change-Id: I458ebac6406a9be0eb4efa804d7f53a0506a6d8b
Reviewed-on: https://chromium-review.googlesource.com/295139
Reviewed-by: Tien Chang <tienchang@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
1 file changed