gradle.home System property should not be required to run test suite

Gradle's build adds -Dgradle.home=roadToNowhere to the test JVM arguments for the benefit of only one test: org.gradle.MainTest .

This makes running the test suite in an IDE environment more difficult. It would be better if the test set the property itself.

I've attached a patch that sets the property in that test and replaces the previous value in the teardown to avoid messy static state sharing inside a test suite.