Add two benchmarks for compaction merge
Add two benchmarks for compaction merge

These benchmarks simulate two different compaction scenarios:
one where the inputs don't really overlap in key-space, and
another where they interleave completely. These two patterns
have different performance characteristics that can be optimized
for.

Change-Id: I289f038323f9cd44ae420df4a3955c398b4fb2c6
Reviewed-on: http://gerrit.ent.cloudera.com:8080/58
Tested-by: jenkins <c14f3aae4f03a600341a3b92ec1ffaac2338cde0@cloudera.com>
Reviewed-by: Matteo Bertozzi <1d5ca967930bde0bdce795acbf71a5e281d2d4e5@cloudera.com>

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