[BEAM-3182] Ensure nexmark model tests produce output

[apilloud]

Some of the Nexmark model tests don't produce any output at the current number of events. This change ensures every test produces some output. It also changes the Query 6 model to match the Query 6 implementation, but it still doesn't match the benchmark specification.

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[apilloud]

R: @kennknowles

[apilloud]

Ping @kennknowles

[kennknowles]

LGTM