runner: Fix process exit timeout.

I flipped the boolean in
https://boringssl-review.googlesource.com/c/boringssl/+/41864 and
applied a timeout in the wrong cases.

Change-Id: I0ea963add45ae627a039f619904dc713d8b0cbf0
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48185
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

ssl/test/runner/runner.go

@@ -1566,7 +1566,7 @@ func runTest(statusChan chan statusMsg, test *testCase, shimPath string, mallocN
 	listener = nil
 
 	var childErr error
-	if !useDebugger() {
+	if useDebugger() {
 		childErr = <-waitChan
 	} else {
 		waitTimeout := time.AfterFunc(*idleTimeout, func() {