[autotest] Improve the pool inventory message.

Based on feedback from a recent deputy, change the pool inventory
message in site_utils/lab_inventory.py to make the expectations
clearer.

BUG=None
TEST=unit tests

Change-Id: I614f7f4a3c0a2095ea4973c1512ebcedae6bde1f
Reviewed-on: https://chromium-review.googlesource.com/275293
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
diff --git a/site_utils/lab_inventory.py b/site_utils/lab_inventory.py
index b5c13ab..97944a7 100755
--- a/site_utils/lab_inventory.py
+++ b/site_utils/lab_inventory.py
@@ -675,10 +675,11 @@
 
 
 _POOL_INVENTORY_HEADER = '''\
-Notice to Infrastructure deputy:  If there are shortages below,
-please take action to resolve them.  If it's safe, you should
-balance shortages by running `balance_pool`.  Detailed instructions
-can be found here:
+Notice to Infrastructure deputies:  If any boards are shown at
+less than full strength, please take action to resolve the issues.
+Once you're satisified that failures won't recur, failed DUTs can
+be replaced with spares by running `balance_pool`.  Detailed
+instructions can be found here:
     http://go/cros-manage-duts
 '''