lorgnette: Add unit tests

Test routines for extracting a device list as well as launching
the scan process.  Also move away for creating a temporary file
for the output of the device list and use a pipe instead.

BUG=chromium:239086
TEST=Unit tests

Change-Id: I6b2a20622cef6e5b15352a5b5702d93b0629e364
Reviewed-on: https://gerrit.chromium.org/gerrit/56315
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
5 files changed