cli: Add debugging message for why binpkg was included/skipped

This debug message helped me figure out why cros deploy --deep was not
working (because we're not including the subslot in `required_slot`).

> DEBUG: Checking packages matching dev-libs/libinput (slot: 0)...
> DEBUG:  Skipping because slot (0/10) != required_slot (0)
> WARNING: No qualified bintree package corresponding to dev-libs/libinput

BUG=b:295550926
TEST=CQ passes

Change-Id: Ic82700f503b00a99e0e3a148dff41f2d3efff2a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/4775883
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Matt Turner <msturner@google.com>
Auto-Submit: Matt Turner <msturner@google.com>
Commit-Queue: Matt Turner <msturner@google.com>
diff --git a/cli/deploy.py b/cli/deploy.py
index 90166db..c8d777b 100644
--- a/cli/deploy.py
+++ b/cli/deploy.py
@@ -796,7 +796,20 @@
             )
             num_processed = 0
             for slot, pkg_info in cp_slots.items():
-                if required_slot and slot != required_slot:
+                if not required_slot:
+                    logging.debug(" Including because no required_slot")
+                elif slot == required_slot:
+                    logging.debug(
+                        " Including because slot (%s) == required_slot (%s)",
+                        slot,
+                        required_slot,
+                    )
+                else:
+                    logging.debug(
+                        " Skipping because slot (%s) != required_slot (%s)",
+                        slot,
+                        required_slot,
+                    )
                     continue
 
                 num_processed += 1