add more exception logging when failing to install xcode

Bug: 370036129
Change-Id: I11597bc56f91e6c19e9c7971beef57e6dba616d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5925758
Commit-Queue: Yue She <yueshe@google.com>
Reviewed-by: Zhaoyang Li <zhaoyangli@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1367808}

Author: Yue She

ios/build/bots/scripts/xcode_util.py

@@ -10,6 +10,7 @@
 import shutil
 import subprocess
 import sys
+import traceback
 
 import iossim_util
 import mac_util
@@ -551,6 +552,7 @@ def install_xcode(mac_toolchain_cmd, xcode_build_version, xcode_path,
   except subprocess.CalledProcessError as e:
     # Flush buffers to ensure correct output ordering.
     sys.stdout.flush()
+    sys.stderr.write(traceback.format_exc())
     sys.stderr.write('Xcode build version %s failed to install: %s\n' %
                      (xcode_build_version, e))
     sys.stderr.flush()