Fix the bug where compaction does not fail when RocksDB can't create a new file.

Summary:
This diff has two fixes.

1. Fix the bug where compaction does not fail when RocksDB can't create a new file.
2. When NewWritableFiles() fails in OpenCompactionOutputFiles(), previously such fail-to-created file will be still be included as a compaction output.  This patch also fixes this bug.
3. Allow VersionEdit::EncodeTo() to return Status and add basic check.

Test Plan:
./version_edit_test
export ROCKSDB_TESTS=FileCreationRandomFailure
./db_test

Reviewers: ljin, sdong, nkg-, igor

Reviewed By: igor

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D25581