More rolling (#2319)

* util: more rolling support

* observe more rolling cnt at the same time
* diff 2 or more dbs

* fix comment

* remove boringutil

* fix py

* util: move 2 py file t

More rolling (#2319)

* util: more rolling support

* observe more rolling cnt at the same time
* diff 2 or more dbs

* fix comment

* remove boringutil

* fix py

* util: move 2 py file to rolling dir

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