[RocksJava] Update BackupableDB and RestoreBackupableDB to 3.8.0.

This change consists of 4 independent tasks and as such 4 Commits:

1.) [RocksJava] Align BackupableDBOptions to other Options implementations
- Updated the BackupableDBOptions functionality to 3.8.0.
- Aligned Options implementation with remaining source code.
- Invented test-case.

2.) [RocksJava] Backupable/Restorable DB update 3.8.0
- GarbageCollectMethod() available.
- GetCorruptedBackups() available.

3.) [RocksJava] Improved BackupableDBTest
- Splitted methods to meaningful tests
- Added tests for additional functionality
- Covered missing parts

4.) [RocksJava] Cleanup Backupable implementations
- Correct usage of isInitialized()
- Adjusted JavaDoc




Differential: https://reviews.facebook.net/D29019