DRILL-6068: Support user/distrib-specific config checks during startup
1. Allows for distrib/user specific checks to be done
2. Place-holder files for distribution and user specific checks
3. Moved JVM Version Check to head of script
Separation of setups into 3 levels
1. Apache Drill (Default)
2. Distribition Specific
3. User-Defined
1 & 2 are mutually exclusive.
3 is additional checks that the user can specify.
