add a test case indicating we reset the stats when starting a new fragment
simplify the code according to Paul's comment
remove delete all statement in DeleteRows.java
add test case to show peak memory usage is larger than current memory usage
simplify test case
add m_ prefix before member, to follow rules
Merge branch 'master' into ENG-6361
clean code according Paul's review
clean code according to Paul's comment
Merge pull request #1443 from VoltDB/ENG-6361

ENG-6361