[libcalamares] Make status of JobQueue queryable

- while the queue is executing (the thread is running jobs) the
  isRunning() method returns true.
- re-work some internals to reset isRunning() before emitting
  finished() signal.

src/libcalamares/JobQueue.cpp

@@ -140,7 +140,7 @@ private:
             m_queue, "failed", Qt::QueuedConnection, Q_ARG( QString, message ), Q_ARG( QString, details ) );
     }
 
-    void emitFinished() { QMetaObject::invokeMethod( m_queue, "finished", Qt::QueuedConnection ); }
+    void emitFinished() { QMetaObject::invokeMethod( m_queue, "finish", Qt::QueuedConnection ); }
 };
 
 JobThread::~JobThread() {}
@@ -195,6 +195,7 @@ JobQueue::start()
     Q_ASSERT( !m_thread->isRunning() );
     m_thread->setJobs( std::move( m_jobs ) );
     m_jobs.clear();
+    m_finished = false;
     m_thread->start();
 }
 
@@ -216,4 +217,11 @@ JobQueue::enqueue( const JobList& jobs )
     emit queueChanged( m_jobs );
 }
 
+void
+JobQueue::finish()
+{
+    m_finished = true;
+    emit finished();
+}
+
 }  // namespace Calamares

src/libcalamares/JobQueue.h

@@ -45,6 +45,11 @@ public:
     void enqueue( const JobList& jobs );
     void start();
 
+    bool isRunning() const { return !m_finished; }
+
+public slots:
+    void finish();
+
 signals:
     void queueChanged( const JobList& jobs );
     void progress( qreal percent, const QString& prettyName );
@@ -57,6 +62,7 @@ private:
     JobList m_jobs;
     JobThread* m_thread;
     GlobalStorage* m_storage;
+    bool m_finished = true;  ///< Initially, not running
 };
 
 }  // namespace Calamares