Replace QtcProcess::stopProcess() by stop() plus waitForFinished

... or nothing, if the process object is destroyed immediately.

Change-Id: I6a1e1928bc49fc20a1c0e0ee9b8f4f723276bbca
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/python/pipsupport.cpp

@@ -95,7 +95,8 @@ void PipInstallTask::run()
 
 void PipInstallTask::cancel()
 {
-    m_process.stopProcess();
+    m_process.stop();
+    m_process.waitForFinished();
     Core::MessageManager::writeFlashing(
         tr("The %1 installation was canceled by %2.")
             .arg(m_package.displayName, m_killTimer.isActive() ? tr("user") : tr("time out")));