Use cherry-pick for uber-merge-strategy
Use cherry-pick for uber-merge-strategy

change merge strategy from merge to cherry-pick, this is to support release branch
add a handle for blank merge
uber/arcanist,chundongwang/arcanist,uber/arcanist,uber/arcanist,uber/arcanist,chundongwang/arcanist,chundongwang/arcanist,chundongwang/arcanist