Gerrit operation - rollback a patch_ set

Back off gerrit Upper patch set, Suppose your goal is to start from patch_set2 -> patch_set1
（ If you encounter a scene that is not only HEAD Different , Even the branches have changed .）

Follow the following methods ：
1 A new path , Separately for downloading patch_set1 and patch_set2
2 Create a new local branch, git checkout -b branchname
3 Use gerrit Medium Reset To Method , First reset To patch_set1,
4 Use gerrit Medium cherry-pick Method , stay patch_set1 On the implementation cherry-pick patch_set2 Method
5 Then modify it patch_set2 The changes to the ,git add
6 git commit --allow-empty,  This step will produce a new commit id
7 get reset HEAD^ , Re execution git commit --amend, Bring the new changes to the previous commit id.
8 Submit