Fix type error caused by using other cookbook attr

I get the following error when using this wrapper cookbook with the
mysql cookbook: https://github.com/opscode-cookbooks/mysql
sha: a2ff53f0ca6deca75aebf6da55ac381194ec7728

Chef::Exceptions::ValidationFailed
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Option port must be a kind of Integer!  You passed "3306".

This fix the wrapper cookbook to use the type it requires.