make profiling work again

The weave SIGINT signal handler was racing the profiler SIGINT signal
handler. So now we a) make the former return instead of exit, and b)
disable the latter, as a result of which the deferred profile.Stop in
weaver/main gets called.

common/signals.go

@@ -24,7 +24,7 @@ func SignalHandlerLoop(ss ...SignalReceiver) {
 			for _, subsystem := range ss {
 				subsystem.Stop()
 			}
-			os.Exit(0)
+			return
 		case syscall.SIGQUIT:
 			stacklen := runtime.Stack(buf, true)
 			Info.Printf("=== received SIGQUIT ===\n*** goroutine dump...\n%s\n*** end\n", buf[:stacklen])

weaver/main.go

@@ -112,6 +112,7 @@ func main() {
 	if prof != "" {
 		p := *profile.CPUProfile
 		p.ProfilePath = prof
+		p.NoShutdownHook = true
 		defer profile.Start(&p).Stop()
 	}