DescribeStackEvents Exception Occurs During Build and Delete

The following exception is thrown during build and delete stages:

```
botocore.exceptions.ClientError: An error occurred (ValidationError) when calling the DescribeStackEvents operation: Stack [myStack] does not exist
```

it appears that stacker attempts to call `DescribeStackEvents` before the stack has actually started creating during `stacker build`. Stacker also appears to call `DescribeStackEvents` after the stack has already been deleted during `stacker delete`.

This doesn't actually cause either of the commands to completely fail but it just throws in exception and the message is displayed in stdout.