Fix DBTest.SuggestCompactRangeTest for disable jemalloc case

Fix DBTest.SuggestCompactRangeTest for disable jemalloc case

Summary: DBTest.SuggestCompactRangeTest fails for the case when jemalloc is disabled, including ASAN and valgrind builds. It is caused by the improvement of skip list, which allocates different size of nodes for a new records. Fix it by using a special mem table that triggers a flush by number of entries. In that way the behavior will be consistent for all allocators.

Test Plan: Run the test with both of DISABLE_JEMALLOC=1 and 0

Reviewers: anthony, rven, yhchiang, kradhakrishnan, igor, IslamAbdelRahman

Reviewed By: IslamAbdelRahman

Subscribers: leveldb, dhruba

Differential Revision: https://reviews.facebook.net/D51423