Restore JUnit reports location

Since the upgrade to Gradle 3, our Bamboo build is failing because it
can't find test reports "at the usual location".

This commit restores the location that Gradle 2 was using until we
upgrade to a version of Bamboo that supports it.

Issue: SPR-14569

Author: snicoll

build.gradle

@@ -160,6 +160,7 @@ configure(allprojects) { project ->
 		// classes with the "$" pattern; otherwise, using -Dtest.single=MyTests to
 		// run MyTests by itself will fail if MyTests contains any inner classes.
 		exclude(["**/Abstract*.class", '**/*$*'])
+		reports.junitXml.destination = file("$buildDir/test-reports")
 	}
 
 	repositories {