deploy_server: Fix server retry message.

Only save server names in the skipped list, instead of tuples describing
them.

BUG=chromium:660173
TEST=None. None at all.

Change-Id: I2d857f8972d816d3e5a4a2a1912f69cc95defe2d
Reviewed-on: https://chromium-review.googlesource.com/407618
Tested-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Don Garrett <dgarrett@chromium.org>
Reviewed-by: Shuqian Zhao <shuqianz@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>
diff --git a/site_utils/deploy_server.py b/site_utils/deploy_server.py
index 3fe1cdd..91c949b 100755
--- a/site_utils/deploy_server.py
+++ b/site_utils/deploy_server.py
@@ -257,7 +257,7 @@
         if not failed or options.cont:
             failed += update_in_parallel(servers, options)
         else:
-            skipped.extend(servers)
+            skipped.extend(s[0] for s in servers)  # Only include server name.
 
     if failed:
         print('Errors updating:')