Summary: Add a script, which checks out changes from a list of tags, build them and load the same data into it. In the last, checkout the target build and make sure it can successfully open DB and read all the data. It is implemented through ldb tool, because ldb tool is available from all previous builds so that we don't have to cross build anything.
Test Plan: Run the script.
Reviewers: yhchiang, rven, anthony, kradhakrishnan, igor
Reviewed By: igor
Subscribers: leveldb, dhruba
Differential Revision: https://reviews.facebook.net/D36639
