TestSuite.xml should wrap event2xml in a Group

[chris-twiner]

With certain input the created xml from event causes

{{{
java.lang.UnsupportedOperationException: unsuitable as hash key
at scala.collection.mutable.Buffer$class.hashCode(Buffer.scala:280)
at scala.collection.mutable.ArrayBuffer.hashCode(ArrayBuffer.scala:26)
at scala.xml.Utility$.hashCode(Utility.scala:263)
at scala.xml.Elem.hashCode(Elem.scala:64)
at scala.collection.mutable.FlatHashTable$class.elemHashCode(FlatHashTable.scal
}}}

Simple fix is to wrap in a Group so line 29 becomes {for (test <- testEvents) yield Group(TestSuite.event2xml(test))} with appropriate import added of course :-).