autotest: Add WEP support to new WiFi test framework

Add support for a couple more settings related to WEP encryption.  Make
it easy to get appropriate shill credentials.

TEST=A test depending on these bits passes.
BUG=chromium:245808

Change-Id: I3e69d5144dbb06e1283c6652a72632819b1ddf13
Reviewed-on: https://gerrit.chromium.org/gerrit/58422
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
2 files changed