Return exit codes from CLI tools

In review of https://github.com/apache/solr/pull/1600, krisden noticed that the exit codes that are suppoed to be returned, never quite got wired in properly.

See https://www.cyberciti.biz/faq/linux-bash-exit-status-set-exit-statusin-bash/ for more info.

This is to track adding that across all our CLI commands.