Summary: OptionChangeMigration() to support FIFO compaction. If the DB before migration is using FIFO compaction, nothing should be done. If the desitnation option is FIFO options, compact to one single L0 file if the source has more than one levels.
Test Plan: Run option_change_migration_test
Reviewers: andrewkr, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D65289
Summary: Add a utility function that trigger necessary full compaction and put output to the correct level by looking at new options and old options.
Test Plan: Add unit tests for it.
Reviewers: andrewkr, igor, IslamAbdelRahman
Reviewed By: IslamAbdelRahman
Subscribers: muthu, sumeet, leveldb, andrewkr, dhruba
Differential Revision: https://reviews.facebook.net/D60783
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