WL4189 Add Handles.pm and use it from My::File::Path to show open handles. Rewrite rmtree to use File::Find so we can get better debug printouts when something fails

- Updated slow_query_log_file_basic and general_log_file basis instead of the func version as
the func version run good but the basic versions fail.
- Sent innodb.test to dev@innodb.com.
- variables.test has differences probably due to a bug in mtr or in the SET statement (see bug#39369).
- general_log_file_basic.test and slow_query_log_file_bsaic.test have differences, which might be 
produced by the new mtr (see bug#38124).

 - fix scheduler bug

 - Rearrange spawn worker code