[Java] Add a basic binding and test for BackupableDB and StackableDB.

Summary:
Add a skeleton binding and test for BackupableDB which shows that BackupableDB
and RocksDB can share the same JNI calls.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17793

java/org/rocksdb/Options.java

@@ -228,6 +228,10 @@ public class Options {
     }
   }
 
+  @Override protected void finalize() {
+    dispose();
+  }
+
   private boolean isInitialized() {
     return (nativeHandle_ != 0);
   }