DRILL-6895: Warnings for license headers checks and wrong license headers in some files - update license-maven-plugin plugin custom mappings - update files licenses headers - update from "/usr/bin/env bash" to "/bin/bash" shebang line in shell script files
* Extended the existing "config" directory concept to create a "site" directory that holds all site-specific files, leaving the Drill directory ($DRILL_HOME) to contain only Drill-provided files. The site directory is handy for all Drill users because it eases upgrades, but is necessary to simplify Drill-on-YARN deployments. Use the --config (for backward compatibility) or --site (more descriptive) option to point to the site directory.
* Moved distribution-specific settings, and Drill defaults, out of drill-env.sh. Now, drill-env.sh contains only user settings, avoiding the need to do multi-way merges on upgrades. Distribution-specific files now reside in a new $DRILL_HOME/conf/distrib-env.sh file.
* Refactored the launch scripts to allow the bulk of setup to be shared between the "classic" Drill daemon script (drillbit.sh) and the new Drill-on-YARN scripts.
* Added a new "run" option to drillbit.sh to allow Drill to run as a child process as needed by tools such as Apache Mesos.
* Changes ensure backward compatibility. Users of earlier releases can upgrade to the release with this fix without doing anything special. Drill will "just work." However, users can optionally clean up the drill-env.sh script, optionally use the site directory, and so on. However these upgrades are not required.