Drill Plugins Handler

• Storage Plugins Handler service is used on the Drill start-up stage and it updates storage plugins configs from
  storage-plugins-override.conf file. If plugins configs are present in the persistence store - they are updated,
  otherwise bootstrap plugins are updated and the result configs are loaded to persistence store. If the enabled
  status is absent in the storage-plugins-override.conf file, the last plugin config enabled status persists.
• 'drill.exec.storage.action_on_plugins_override_file' Boot option is added. This is the action, which should be
  performed on the storage-plugins-override.conf file after successful updating storage plugins configs.
  Possible values are: "none" (default), "rename" and "remove".
• The "NULL" issue with updating Hive plugin config by REST is solved. But clients are still being instantiated for disabled
  plugins - DRILL-6412.
• "org.honton.chas.hocon:jackson-dataformat-hocon" library is added for the proper deserializing HOCON conf file
• additional refactoring: "com.typesafe:config" and "org.apache.commons:commons-lang3" are placed into DependencyManagement
  block with proper versions; correct properties for metrics in "drill-override-example.conf" are specified

Please find details from design overview document:
https://docs.google.com/document/d/14JKb2TA8dGnOIE5YT2RImkJ7R0IAYSGjJg8xItL5yMI/edit?usp=sharing