[autotest] Add packages required by unittests.

pyudev is needed by client/cros/rf/config_unittest.py
dnspython is needed by server/cros/recall_test.py

BUG=chromium-os:37989
TEST=./build_externals.py ran successfully

Change-Id: I84e70ec3ea9afe1d005afc962aaf244197363b4c
Reviewed-on: https://gerrit.chromium.org/gerrit/43246
Tested-by: Alex Miller <milleral@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Alex Miller <milleral@chromium.org>
1 file changed