quoting support for to_dict

[clumsy]

Description

to_dict used to parse env key-value pairs does not allow using = as part of the value.

Motivation/Background

This means we cannot set values for NCCL_IB_HCA for example: https://docs.nvidia.com/deeplearning/nccl/user-guide/docs/env.html#id8

Detailed Proposal

In addition to existing functionality add support for quoted values to escape all special symbols: ;, , and =

Alternatives

Hard code the env variables in, say, Dockerfile

Additional context/links

[clumsy]

For you consideration @kiukchung, @d4l3k, @tonykao8080