Add print gsutil ls output for git_cache

Bug: 1370443
Change-Id: I113169a0fdfb3ea87f5f27ba066cce93b3ee6c91
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3938922
Commit-Queue: Joanna Wang <jojwang@chromium.org>
Reviewed-by: Gavin Mak <gavinmak@google.com>

git_cache.py

@@ -520,6 +520,7 @@ class Mirror(object):
 
     # ls_out lists contents in the format: gs://blah/blah/123...
     _, ls_out, _ = gsutil.check_call('ls', self._gs_path)
+    self.print('ran "gsutil ls %s": %s' % (self._gs_path, ls_out))
 
     # Check to see if folder already exists in gs
     ls_out_set = set(ls_out.strip().splitlines())