[crashlog] Print the actual exception in the CommandReturnObject

Before:

  error: python exception <class 'AttributeError'>

After:

  error: python exception: 'DarwinImage' object has no attribute 'debugger'

lldb/examples/python/crashlog.py

@@ -849,8 +849,8 @@ def save_crashlog(debugger, command, exe_ctx, result, dict):
 def Symbolicate(debugger, command, result, dict):
     try:
         SymbolicateCrashLogs(shlex.split(command))
-    except:
-        result.PutCString("error: python exception %s" % sys.exc_info()[0])
+    except Exception as e:
+        result.PutCString("error: python exception: %s" % e)
 
 
 def SymbolicateCrashLog(crash_log, options):