Summary:
My understanding is that the purpose of write stall triggers are to wait for auto-compaction to catch up. Without auto-compaction, we don't need to stall writes.

Also with this diff, flush/compaction conditions are recalculated on dynamic option change. Previously the conditions are recalculate only when write stall options are changed.

Test Plan: See the new test. Removed two tests that are no longer valid.

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D61437