Fixed failing tests for /stream.

Descriptions of the changes in this PR:

Fixed tests for /stream, RocksDB initialization.
Same as #2551 but for master branch

### Motivation

Tests were failing with " “java.lang.UnsatisfiedLinkError: 'long org.rocksdb.LRUCache.newLRUCache(long, int, boolean, double)'”".

### Changes

Fixed following suggestion form facebook/rocksdb#6789
Added
`    static {
        RocksDB.loadLibrary();
    }`
to extract the native library from the jar file etc.

Master Issue: #2550

Reviewers: Enrico Olivelli <eolivelli@gmail.com>

This closes #2554 from dlg99/master-streams-tests

(cherry picked from commit 73b4cd4)
Signed-off-by: Enrico Olivelli <eolivelli@apache.org>

stream/statelib/src/main/java/org/apache/bookkeeper/statelib/impl/kv/RocksdbKVStore.java

@@ -127,6 +127,10 @@ public class RocksdbKVStore<K, V> implements KVStore<K, V> {
     // rocksdb checkpointer
     private RocksCheckpointer checkpointer;
 
+    static {
+        RocksDB.loadLibrary();
+    }
+
     public RocksdbKVStore() {
         // initialize the iterators set
         this.kvIters = Collections.synchronizedSet(Sets.newHashSet());