RUBY-661 add support and tests for maxTimeMS

This should work as another test but the sleep command seems broken/deprecated:

```ruby
def test_cursor_timeout_command
  admin = @@connection.db('admin')
  cursor = admin.command({ :sleep => { :w => false, :secs => 1 } })
  cursor.max_time(100);

  assert_raise ExecutionTimeout do
    cursor.to_a
  end
end
```