CI logging improvements

This PR is a first proposal to improve parsing of the Bio-Formats CI jobs. Idea of this set of commits is to:

1. generate manageable log files (~250MB / 12 threads ~ 20MB per log file)
1. simplify failure multi-threaded log parsing
1. implement a more systematic way to parse for failures,

Changes proposed as part of this PR are:
- using sifting to split the log  file per thread (to simplify parsing)
- removing thread information from the logfile content (should be in the title) and add debug level
- logging  metadata failures at the ERROR level.
With this, a simple comand like `grep -B 20 ERROR bio-formats*.log` should list failed tests and identify the faulty files.

Additional tasks that could be implemented as part of this PR if it is sensible:
- [x] move `bio-formats-*.log` to `target` and simplify the `ant clean` target
- [x]  refactor the stdout appender to display test results and keep the details in the logfiles