[autotest] Require lock reason to lock device

When locking a device, a locking reason now must be provided.
This applies to both adding a new device, and modifying an
existing device from both the web frontend and the atest
command-line tool.

BUG=chromium:336805
DEPLOY=migrate
TEST=Tested adding locked/unlocked devices and locking/unlocking devices
from both the web frontend and using the 'atest host ...' command-line tools.

Change-Id: I3a8cd8891a2999f026dd709ae8a79e2b8cbc251a
Reviewed-on: https://chromium-review.googlesource.com/267595
Tested-by: Matthew Sartori <msartori@chromium.org>
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Matthew Sartori <msartori@chromium.org>
diff --git a/frontend/afe/models_test.py b/frontend/afe/models_test.py
index 8219755..6865bf5 100755
--- a/frontend/afe/models_test.py
+++ b/frontend/afe/models_test.py
@@ -434,6 +434,7 @@
                                        'only_if_needed': False,
                                        'platform': False}],
                            'leased': False,
+                           'lock_reason': '',
                            'lock_time': None,
                            'locked': False,
                            'protection': 0,