skip apikey_check error when auto_create_bucket and bucket doesn't exist...

This pull request resolves issue #60.
How about like this?

```rb
rescue AWS::S3::Errors::NoSuchBucket
  # ignore No such bucket error for auto_create_bucket
rescue
  raise "can't call S3 API. Please check your aws_key_id / aws_sec_key or s3_region configuration"
end
```

This way seems more clear than `unless &&` pair.