Support use different parameters to run the same method multi-times in testng.xml.

Hi Cbeust,

This features will support use different parameters to run the same method multi-times in testng.xml.
`<class name="a.b.DemoTest">
    <methods>
        <include name="test001">
            <parameter name="userName" value="A"></parameter>
        </include>
        <include name="test001">
            <parameter name="userName" value="B></parameter>
        </include>
    </methods>
</class>`
The test method test001 will run twice use parameter value A and B.

This feature is very useful for us. I think this is also useful for others.
Could you help us to merge it.

 I implement it use the solution you said at here: https://github.com/cbeust/testng/pull/242
There are a few things I don't like in this pull request. The correct way of handling this would be to have XmlSuite/Test/Class/Include return a ListMultiMap of parameters instead of a Map, so that we can have, for example, a multi map of { "num", [1, 2] }. Then the current parameter engine would make this work magically with little changes.

Br,
Cen