public ServerLocation getNextOpServerLocation() {
    Connection conn = connectionManager.borrowConnection(serverTimeout);
    try {
      return conn.getServer();
    } finally {
      connectionManager.returnConnection(conn);
    }
  }
execute the given op on the given server. If the server cannot be reached, sends a
TXFailoverOp, then retries the given op

@param loc the server to execute the op on
@param op the op to execute
@return the result of execution
geode-core/src/main/java/org/apache/geode/cache/client/internal/OpExecutorImpl.java