Gradle clean does not remove all generated files

**Sebb** ([Bug 63914](https://bz.apache.org/bugzilla//show_bug.cgi?id=63914&redirect=false)):
The following sequence:

./gradlew createDist
./gradlew clean

should leave the directory as it was originally.

However, that is not the case: a comparison shows:

Only in ../jmeter-build: .gradle
Only in ../jmeter-build: build
Only in ../jmeter-build/buildSrc: .gradle
Only in ../jmeter-build/buildSrc: build
Only in ../jmeter-build/buildSrc/subprojects/batchtest: build
Only in ../jmeter-build/lib/junit: test.jar

It may be OK to leave the .gradle and build items, but test.jar should definitely not be left behind.

Severity: normal
OS: All