Minor fixes & tweaks to improve error handing in preparation for BBSim REST API pull request.

Added comments to reduce golint warnings.

Main contributors: Pragya Arya, Vishesh Prasidh

Change-Id: I6f0b67a39dd0b8da0288306ac4f66098df53b18d
diff --git a/core/tester.go b/core/tester.go
index 279d2c8..2349fae 100644
--- a/core/tester.go
+++ b/core/tester.go
@@ -86,7 +86,10 @@
 func (tm *TestManager) StartTester (key device.Devkey, t *Tester) error {
 	logger.Debug("StartTester called with key:%v", key)
 	if t.Mode == DEFAULT {
-		//Empty
+		_, child := errgroup.WithContext(tm.ctx)
+		child, cancel := context.WithCancel(child)
+		t.ctx = child
+		t.cancel = cancel
 	} else if t.Mode == AAA || t.Mode == BOTH {
 		eg, child := errgroup.WithContext(tm.ctx)
 		child, cancel := context.WithCancel(child)