[Test] Properly handle output from separate jvm instance in box tests

compiler/tests-common-new/tests/org/jetbrains/kotlin/test/backend/handlers/JvmBoxRunner.kt

@@ -210,12 +210,23 @@ class JvmBoxRunner(testServices: TestServices) : JvmBinaryArtifactHandler(testSe
             classPath.joinToString(File.pathSeparator, transform = { File(it.toURI()).absolutePath }),
             mainFqName,
         )
-        val process = ProcessBuilder(command).inheritIO().start()
+        val process = ProcessBuilder(command).start()
         process.waitFor(1, TimeUnit.MINUTES)
-        process.outputStream.flush()
-        return when (process.exitValue()) {
-            0 -> "OK"
-            else -> "External process completed with error. Check the build log"
+        return try {
+            when (process.exitValue()) {
+                0 -> "OK"
+                else -> buildString {
+                    for (stream in listOfNotNull(process.inputStream, process.errorStream)) {
+                        stream.bufferedReader().lines().forEach { appendLine(it) }
+                    }
+
+                    if (this.isEmpty()) {
+                        appendLine("External process completed with error. Check the build log")
+                    }
+                }
+            }
+        } finally {
+            process.outputStream.flush()
         }
     }