Show actual exception when deletion fails.

python/servo/bootstrap_commands.py

@@ -16,6 +16,7 @@
 import re
 import subprocess
 import sys
+import traceback
 import urllib2
 import glob
 
@@ -318,6 +319,7 @@ def get_size(path):
                                         try:
                                             delete(crate_path)
                                         except:
+                                            print(traceback.format_exc())
                                             print("Delete %s failed!" % crate_path)
                             else:
                                 print("Would remove `{}`{} package from {}".format(*print_msg))