worlddump: log command failure details

If a command we trigger fails for some reason, it's worth logging
details about the failure (like return code).

Change-Id: Ib19aa474eccdd11e138a4f55e125935b621bca05
diff --git a/tools/worlddump.py b/tools/worlddump.py
index 01f601c..72a257f 100755
--- a/tools/worlddump.py
+++ b/tools/worlddump.py
@@ -58,8 +58,8 @@
     try:
         subprocess.check_call(cmd, shell=True)
         print
-    except subprocess.CalledProcessError:
-        print "*** Failed to run: %s" % cmd
+    except subprocess.CalledProcessError as e:
+        print "*** Failed to run '%(cmd)s': %(err)s" % {'cmd': cmd, 'err': e}
 
 
 def _find_cmd(cmd):