Fix Client.operations

Non-versioned client classes (like `AWS::EC2::Client`) were returning an empty list of operations:

```ruby
# bad
AWS::EC2::Client.operations #=> []
```

However, if you construct the versioned client, it returns the correct list

```ruby
# good
AWS::EC2::Client::V20130715.operations #=> [...]
```

This patch causes the client class to ask the default versioned client class for its list of operations.