ConcurrentRepackTest: Open RevWalk in try-with-resource

Change-Id: Idc7b7bbdc1df05372b873cbe4c495474f3ffd64b
Signed-off-by: David Pursehouse <david.pursehouse@sonymobile.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/internal/storage/file/ConcurrentRepackTest.java

 
 	private RevObject parse(final AnyObjectId id)
 			throws MissingObjectException, IOException {
-		return new RevWalk(db).parseAny(id);
+		try (RevWalk rw = new RevWalk(db)) {
+			return rw.parseAny(id);
+		}
 	}
 
 	private File[] pack(final Repository src, final RevObject... list)
 
 	private RevObject writeBlob(final Repository repo, final String data)
 			throws IOException {
-		final RevWalk revWalk = new RevWalk(repo);
 		final byte[] bytes = Constants.encode(data);
 		final ObjectId id;
 		try (ObjectInserter inserter = repo.newObjectInserter()) {
 		} catch (MissingObjectException e) {
 			// Ok
 		}
-		return revWalk.lookupBlob(id);
+		try (RevWalk revWalk = new RevWalk(repo)) {
+			return revWalk.lookupBlob(id);
+		}
 	}
 }