DeviceShell tests: Use ProcessLauncher for shell process

It looks like after recent switch to QProcess impl for
Utils::Process, the DeviceShell::m_shellProcess blocks
in DeviceShell::installShellScript() on a call to
m_shellProcess->waitForReadyRead(5000). Until it's solved,
bring back the ProcessLauncher impl for the shell process
to unlock the CI tests.

Amends a53dfaf623

Change-Id: I085ea5c1ae4f169c7c77acb8702ed48de0a95bac
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/libs/utils/deviceshell.cpp

@@ -163,6 +163,8 @@ CommandLine DeviceShell::createFallbackCommand(const CommandLine &cmd)
 expected_str<void> DeviceShell::start()
 {
     m_shellProcess = std::make_unique<Process>();
+    // FIXME: This shouldn't be needed, it's a temporary workaround.
+    m_shellProcess->setProcessImpl(ProcessImpl::ProcessLauncher);
     connect(m_shellProcess.get(), &Process::done, m_shellProcess.get(),
             [this] { emit done(m_shellProcess->resultData()); });
     connect(&m_thread, &QThread::finished, m_shellProcess.get(), [this] { closeShellProcess(); }, Qt::DirectConnection);