make DropWritesFlush deterministic

Summary:
TEST_WaitForFlush should wait until it sees error when parameter is set
to true so we don't need to loop and timeout

Test Plan: ROCKSDB_TESTS=DropWritesFlush ./db_test

Reviewers: sdong, igor

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28419
Make PartialCompactionFailure Test more robust again.

Summary:
Make PartialCompactionFailure Test more robust again by
blocking background compaction until we simulate the
file creation error.

Test Plan:
export ROCKSDB_TESTS=PartialCompactionFailure
./db_test

Reviewers: sdong, igor, ljin

Reviewed By: ljin

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28431
Correctly test both compaction styles in CompactionDeletionTriggerReopen

Summary:
CompactionDeletionTriggerReopen wasn't actually testing universal
compaction.

Test Plan: db_test

Reviewers: sdong, igor

Reviewed By: igor

Subscribers: dhruba

Differential Revision: https://reviews.facebook.net/D28443