Add `testReportsDirectory` setting to allow output directory for
JUnitXmlTestsListener to be configured.
Add `testReportSettings` which provides defaults values:
- by default this uses the build configuration name as a prefix so
`target/test-reports` for `Test` config, but `target/it-reports`
for `IntegrationTest` (previously this was hardcoded to always
use `target/test-reports`). To override this set e.g.
`Test / testReportsDirectory := target.value / "my-custom-dir"`
- the `JunitXmlTestsListener` is now only attached to the `Test`
and `IntegrationTest` configs by default (previously it was added
to the global configuration object). Any configs which inherit
from one of these will continue to have the listener attached;
but completely custom configurations will need to re-add with:
`project.settings(testReportSettings)`
Fixes#2853
Ashley Mercer