autotest: Change DHCP Field and Option to namedtuple

This lets us use these objects as fields in a dictionary without
implementing a lot of very tedious operation methods.  This in turn
fixes this nonsense where we use the names of Options in some places and
the Option numbers in others.

BUG=chromium-os:34417
TEST=unittests pass, autotest tests pass

Change-Id: I971b98505d0a1e95fd40e6ea3557a7dee63dfa62
Reviewed-on: https://gerrit.chromium.org/gerrit/33151
Commit-Ready: Christopher Wiley <[email protected]>
Reviewed-by: Christopher Wiley <[email protected]>
Tested-by: Christopher Wiley <[email protected]>
4 files changed