autotest: Test dhcpcd handling of lease expiration

Check that dhcpcd sends expected messages when leases are nearing their
expiration.

Set up a situation where we have a lease on an IP address granted by a
DHCP server.  The lease is then allowed to expire by the DHCP server
with no response.  Check that dhcpcd attempts to renew the lease.
Ideally we'd also check that shill deconfigures the lease, but
unfortunately, shill doesn't do that right now, a known bug.

BUG=chromium-os:33764
TEST=This is the test

Change-Id: I224d6187db66904cb7e87ec289c761e866bbb01b
Reviewed-on: https://gerrit.chromium.org/gerrit/33633
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Ready: Christopher Wiley <wiley@chromium.org>
3 files changed