Add a delay for the dhcp server on some APs.

Some of the APs need additional time before the DHCP server is ready.
If the DUT attempts to connect before then, a failure is recorded
which generates a false failure.

BUG=chrome-os-partner:37686
TEST=Manual; ran it

Change-Id: I85d658025dc29ac646e937027f5d55f46be73838
Reviewed-on: https://chromium-review.googlesource.com/264868
Tested-by: Kris Rambish <krisr@chromium.org>
Reviewed-by: Tien Chang <tienchang@chromium.org>
Commit-Queue: Kris Rambish <krisr@chromium.org>
Trybot-Ready: Kris Rambish <krisr@chromium.org>
5 files changed