Add type parameters in OutboundConnectionQueueTest

The use of PowerMock's Whitebox without type parameters led to compile
problems with Java 6.
[FLINK-1032] Allow Access of Nested Fields in POJO Field Expressions

This extends the PojoTypeInfo to allow key expressions like "foo.bar".
Right now the implementation is not very pretty but without turning to
code generation this is the way to do it, IMHO.
Fix bug with using POJO type as return value of key selector function

Also fix using field expressions for ReduceGroup Operator