proc/test: improve TestStepParked

It was possible for TestStepParked to pick a runtime goroutine and
attempt to step it. Nothing guarantees that a goroutine other than the
ones we are using to run the code would actually ever resume before the
end of the program.

This makes the test more discerning in its choice of goroutines.

pkg/proc/proc_test.go

@@ -1861,13 +1861,23 @@ func TestStepParked(t *testing.T) {
 			assertNoError(err, t, "GoroutinesInfo()")
 
 			for _, g := range gs {
-				if g.thread == nil {
+				if g.thread == nil && g.CurrentLoc.Fn != nil && g.CurrentLoc.Fn.Name == "main.sayhi" {
 					parkedg = g
 					break LookForParkedG
 				}
 			}
 		}
 
+		t.Logf("Parked g is: %v\n", parkedg)
+		frames, _ := parkedg.Stacktrace(20)
+		for _, frame := range frames {
+			name := ""
+			if frame.Call.Fn != nil {
+				name = frame.Call.Fn.Name
+			}
+			t.Logf("\t%s:%d in %s (%#x)", frame.Call.File, frame.Call.Line, name, frame.Current.PC)
+		}
+
 		assertNoError(p.SwitchGoroutine(parkedg.ID), t, "SwitchGoroutine()")
 		p.ClearBreakpoint(bp.Addr)
 		assertNoError(p.Step(), t, "Step()")