autotest: Make Dhcp Options optional

Stop building certain magical options into the packet creation
factories, and move that creation logic out into the handlers.  It's
impossible to anticipate every possible option you might want in a test,
so the decision should be entirely up to the test.

BUG=chromium-os:34417
TEST=Unit test still runs, autotests still pass

Change-Id: I17e3415136cef64c48c9c1f2db53440c0d75a3b0
Reviewed-on: https://gerrit.chromium.org/gerrit/33160
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Christopher Wiley <wiley@chromium.org>
3 files changed