ENG-5884: Delete unwanted unloadable generation.
ENG-5884: Delete empty generation directory.
ENG-5884: Print number of files only.
ENG-5884: nullcheck
Merge pull request #1152 from VoltDB/ENG-5884

Eng 5884
Merge branch 'master' of github.com:VoltDB/voltdb into ENG-5571-subquery