TS-1805: fix conversion when pass value to statVarSet()

The result from NodeStatEval()/ClusterStatEval() could have different type
compare to the token type of m_node_dest/m_cluster_dest.

So we should do conversion in statVarSet() when they are different.

Signed-off-by: Yunkai Zhang <qiushu.zyk@taobao.com>
Signed-off-by: Zhao Yongming <ming.zym@gmail.com>