Describe the bug
fc22d96
This commit (after ver 0.15.2) makes all the environment variables quoted in mpi based training.
For example, module cannot be imported correctly because PYTHONPATH should be (some path) but "(some path)".

To Reproduce
Steps to reproduce the behavior:

1. Run multi-node training with mpi (e.g., openmpi)

Expected behavior
Environment variable should be quoted when it is necessary

ds_report output
N/A

Screenshots
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System info (please complete the following information):
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Launcher context
deepspeed, MPI

Docker context
N/A

Additional context
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