JMX_PORT is not used

Although JMX_PORT is assigned and JMX_MODE=local, (defaults) JMX server is not started

**To Reproduce**
Steps to reproduce the behavior:
1. Start IotDB cluster node with default settings.
2. Using bash, look if 31999 port is open
3. In logs, there is a phrase like
`[main] WARN o.a.i.d.s.StartupChecks:38 - iotdb.jmx.port missing from iotdb-env.sh(Unix or OS X, if you use Windows, check conf/iotdb-env.bat) `

**Expected behavior**
JMX server to started

**Kubernetes Environment**
- Apache IotDB 0.12.3

**Additional context**
I also tried to set JMX_PORT, JMX_MODE and iotdb.jmx.port as envrionment variables without success

复现默认的 cluster-node 启动，并检查 31999 端口以及 StartupChecks 关于 iotdb.jmx.port 的警告。首先阅读 iotdb-env.sh 和 conf/iotdb-env.bat，然后跟踪 JMX_PORT、JMX_MODE 和 iotdb.jmx.port 的读取方式。完成的标准是：默认配置能够在预期端口启动 JMX 服务器，而无需手动更改环境变量。

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