Add missing save/re-read cluster configuration

.. in LUClusterSetParams. Since _SetFileStorageDir updates the 'cluster'
variable directly, we need to re-read it and then save later (the other
calls use the configuration directly).
Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>

lib/cmdlib/cluster.py

@@ -1485,10 +1485,14 @@ class LUClusterSetParams(LogicalUnit):
     self.cfg.Update(self.cluster, feedback_fn)
 
     self._SetVgName(feedback_fn)
+
+    self.cluster = self.cfg.GetClusterInfo()
     self._SetFileStorageDir(feedback_fn)
+    self.cfg.Update(self.cluster, feedback_fn)
+
     self._SetDrbdHelper(feedback_fn)
 
-    # re-read the fresh configuration
+    # re-read the fresh configuration again
     self.cluster = self.cfg.GetClusterInfo()
 
     if self.op.hvparams: