Refactored integration tests

Added internal/rc to remote control a Syncthing process and made the
"awaiting sync" determination reliable.

test/httpstress_test.go

@@ -29,16 +29,9 @@ func TestStressHTTP(t *testing.T) {
 	}
 
 	log.Println("Starting up...")
-	sender := syncthingProcess{ // id1
-		instance: "2",
-		argv:     []string{"-home", "h2"},
-		port:     8082,
-		apiKey:   apiKey,
-	}
-	err = sender.start()
-	if err != nil {
-		t.Fatal(err)
-	}
+
+	p := startInstance(t, 2)
+	defer checkedStop(t, p)
 
 	// Create a client with reasonable timeouts on all stages of the request.
 
@@ -147,9 +140,4 @@ func TestStressHTTP(t *testing.T) {
 	if firstError != nil {
 		t.Error(firstError)
 	}
-
-	_, err = sender.stop()
-	if err != nil {
-		t.Error(err)
-	}
 }