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