[autotest] Fix lab_inventory to properly report its metrics.

The lab_inventory script has been failing to report the metric for
DUTs in repair loops.  This adds a call to `metrics.Flush()` to make
sure that the metrics get reported.

BUG=chromium:775199
TEST=None

Change-Id: Ia09c0e06c5c1b013af470cdf4ce01418e50ee617
Reviewed-on: https://chromium-review.googlesource.com/907213
Reviewed-by: Paul Hobbs <phobbs@google.com>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
diff --git a/site_utils/lab_inventory.py b/site_utils/lab_inventory.py
index 3cde9ce..87649e0 100755
--- a/site_utils/lab_inventory.py
+++ b/site_utils/lab_inventory.py
@@ -1364,6 +1364,7 @@
             with site_utils.SetupTsMonGlobalState(
                     'repair_loops', short_lived=True, auto_flush=False):
                 _perform_inventory_reports(arguments)
+            metrics.Flush()
         else:
             _perform_inventory_reports(arguments)
     except KeyboardInterrupt: