[core] Merge Pull Request #371 from 'YCSB-hdr-default/master'
- *incompatible* Default measurement changed from histogram to hdrhistogram Users who want previous behavior can set the 'measurementtype' property to 'histogram'
- *incompatible* Reported 95th and 99th percentile latencies now in microseconds (previously in milliseconds)
Conflicts:
core/src/main/java/com/yahoo/ycsb/measurements/OneMeasurementHdrHistogram.java
closes #371