Make net/test/test_server correctly report timeouts.

Make net/test/test_server correctly report timeouts.

poll() returns 0 on a timeout, and doesn't set errno in that case,
so it makes no sense to use PLOG on a timeout.

Also, this change prints the number of bytes already read, to help distinguish
between a case where we never receive anything from the server, and a case
where we do receive response but not all of it, and the rest gets stuck
for some reason (buffering?).

BUG=96594
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=175204

[Ryan Sleevi, 2013-01-04 21:45:45]

lgtm