CMake: Enable switching between different temporary CMake configurations

This got broken when moving the BuildDirManager from the BuildConfiguration
into the Project itself.

As a side-effect this patch also fixes the persisting of cmake state.

Task-number: QTCREATORBUG-19075
Change-Id: I1fc696097b09f5285e67f20885eb1fa27504990b
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/plugins/cmakeprojectmanager/builddirparameters.h

@@ -52,6 +52,7 @@ public:
 
     Utils::FileName sourceDirectory;
     Utils::FileName buildDirectory;
+    Utils::FileName workDirectory; // either buildDirectory or a QTemporaryDirectory!
     Utils::Environment environment;
     CMakeTool *cmakeTool = nullptr;