It is a common practice for tools to have user-default settings in the well-defined location.

The main goal is to provide better experience for users, allowing them to customize jtreg execution modes.

jtreg might be improved to use
~/.jtreg/jtreg.conf
and allow to redefine some settings.
The most useful cases are:
1)disable report-generation, that is quite-long
2)set verbosity level appropriate for user
and other

The option --skip-default might be added to ignore these setting if needed for Makefile execution. While might be it is not needed,really.

The workaround would be to use wrapping scripts, but adding this into the user-defined properties simplifies this approach.