* siri/logger-fix:
  [logger] Update documentation
  [logger] Adjust priority settings in test
  [logger] Unregister handler names before terminating
  [logger] Stress overload_kill tests in disk_log handler

* peppe/kernel/logger_updates:
  [logger] Correct documentation
  [logger] Update handler documentation
  [logger] Fix test suite compilation warnings
  [logger] Fix failing tests
  [logger] Change overload_kill_restart_after value to infinity
  [logger] Change name of function sync/1 to filesync/1
  [logger] Reset logger config after tests
  [logger] Don't delete log file of failing test cases
  [logger] Set up priority for processes generatig test bursts
  [logger] Stress overload_kill tests a bit more
  [logger] Remove some compiler warnings in test suites
  [logger] Sort keys when testing formatter template
  [logger] Skip test involving file access rights on windows
  [logger] Skip some overload protection tests when using dirty schedulers

 Included config files relative to sys.config directory

OTP-15137

Change the way included config files are searched in sys.config.
Search first relative to sys.config directory, then relative
to current working directory, for backward compatibility.

This permit same result when using a sys.config file in a release
or starting manually a node with -config.

Credit to Siri Hansen for test case.