Petascope_RasImplementation should be singleton in executeRasqlQuery()

[Bang Pham Huu]

Every time executeRasqlQuery invoked, this object is created while username and password can change only when Petascope restarts.

 RasImplementation impl = new 
 RasImplementation(ConfigManager.RASDAMAN_URL);
        impl.setUserIdentification(username, password);

So RasImplementation should be a singleton to be reused.

[Bang Pham Huu]

Code like this will be thread-safe.

public class CassandraAstyanaxConnection {

    private CassandraAstyanaxConnection(){ }        

    private static class Holder {
       private static final CassandraAstyanaxConnection INSTANCE = new CassandraAstyanaxConnection();
    }

    public static CassandraAstyanaxConnection getInstance() {
        return Holder.INSTANCE;
    }
    // rest of class omitted
}