cros_run_unit_tests: make disabled test list a little nicer

When we show the list of disabled tests, it looks like:
11:50:02: WARNING: The following packages do not have tests:
11:50:02: WARNING: app-benchmarks/xfstests
app-crypt/trousers
chromeos-base/attestation-client
...
11:50:02: INFO: RunCommand: sudo ...

The formatting makes it easy to miss the first one and then lose the
rest in the log.  Tweak the output slightly to look like:
11:50:02: WARNING: The following packages do not have tests:
  app-benchmarks/xfstests
  app-crypt/trousers
  chromeos-base/attestation-client
  ...
11:50:02: INFO: RunCommand: sudo ...

BUG=chromium:996480
TEST=`cros_run_unit_tests --board betty` looks a bit nicer

Change-Id: I3a32affbb6eeccddb9386a665a1d1d35742a55c9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1778715
Reviewed-by: Chris McDonald <cjmcdonald@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/cros_run_unit_tests.py b/scripts/cros_run_unit_tests.py
index 039afbb..cfecf47 100644
--- a/scripts/cros_run_unit_tests.py
+++ b/scripts/cros_run_unit_tests.py
@@ -112,8 +112,8 @@
   pkg_with_test = portage_util.PackagesWithTest(sysroot, packages)
 
   if packages - pkg_with_test:
-    logging.warning('The following packages do not have tests:')
-    logging.warning('\n'.join(sorted(packages - pkg_with_test)))
+    logging.warning('The following packages do not have tests:\n  %s',
+                    '\n  '.join(sorted(packages - pkg_with_test)))
 
   if opts.pretend:
     print('\n'.join(sorted(pkg_with_test)))