ENG-7325 sqlcmd refactor
Fix sqlcmd false error code after using stdin.
Merge branch 'master' into ENG-7325-sqlcmd-refactor-squashed
Merge pull request #1876 from VoltDB/ENG-7325-sqlcmd-refactor-squashed

Eng 7325 sqlcmd refactor squashed - will address review feedback w/ future commits.