VcsCommand: Extract some methods for further usage

Change-Id: I385a02d773527a73bbd7fff0a40a40db476a70b8
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/vcsbase/vcscommand.h

@@ -46,6 +46,7 @@ private:
     QFutureInterface<void> *m_future;
     QMutex *m_futureMutex = nullptr;
     friend class VcsCommand;
+    friend class Internal::VcsCommandPrivate;
 };
 
 class VCSBASE_EXPORT CommandResult