Implement ProcessLauncherImpl::waitFor*() methods

Change-Id: I68b77300e77701e527079cecee4d92411f15be14
Reviewed-by: hjk <hjk@qt.io>

src/tools/processlauncher/launchersockethandler.cpp

@@ -232,6 +232,7 @@ void LauncherSocketHandler::handleStartPacket()
     process->setWorkingDirectory(packet.workingDir);
     process->setProcessChannelMode(packet.mode);
     process->start(packet.command, packet.arguments);
+    process->closeWriteChannel();
 }
 
 void LauncherSocketHandler::handleStopPacket()