Improvements in InMemoryDataTree benchmarking.

Added profile "benchmarks" into Yangtools parent pom to automatically run benchmarks with Yangtools build.
Added maven build plugin into benchmarks project for running JMH benchmarks via Maven execution.
Added minor changes to specify Fork and Warmup counts for InMemoryDataTree benchmark.

Change-Id: I8897a75a1cbed6a16fab13c8b7b4d68e61d88db6
Signed-off-by: Lukas Sedlak <lsedlak@cisco.com>
Merge "Improvements in InMemoryDataTree benchmarking."