[Bugfix]: Fix communication Timeout error in safety-constrained distributed System

[ZwwWayne]

This PR fixes the Timeout bug of vLLM in https://www.volcengine.com/.

In some distributed systems, such as volc with safety protection, the machine has only a few ports that can be used for distributed communication. In such a case, the current logic to find an available port will not work and cause an NCCL Timeout error (i.e., the current code finds many 'available' ports that are essentially not available due to the protection strategies in volc). As a workaround, this PR allows the user to set the available port used in vllm.

An example of usage in the Volc engine with vLLM is as below.

export HOST_IP=${MLP_HOST}
export VLLM_PORT=${MLP_PORT:-2222}

The user only needs to set the environment variable before launching the inference engine with this PR in the launch scripts. The $MLP_HOST and $MLP_PORT are set during machine initialization.

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[youkaichao]

LGTM, please address the comments.

[youkaichao]

LGTM