Class-cast exceptions caused by TestUtil.getSplits() and TestUtil.getGuidePostsList()

These test utility methods are trying to convert a PrepareStatement object initiated by the current JDBC Connection into a PhoenixPreparedStatement. While we have switched to Calcite-Phoenix connections for tests, the PreparedStatement created by the connection will no longer be a PhoenixPreparedStatement object, so we need to get the original PhoenixConnection object for such util methods.

        String query = "SELECT /*+ NO_INDEX */ COUNT(*) FROM " + tableName + whereClause;
        PhoenixPreparedStatement pstmt = conn.prepareStatement(query).unwrap(PhoenixPreparedStatement.class);