[ISSUE-1030] Handle module file path when loading from different OS

[parano]

Description

Discussed offline with @yubozhao on refactoring the fix for #1030

cc @yubozhao could you take over the PR and add the remaining CI part?

Motivation and Context

How Has This Been Tested?

Types of changes

• Breaking change (fix or feature that would cause existing functionality to change)
• New feature and improvements (non-breaking change which adds/improves functionality)
• Bug fix (non-breaking change which fixes an issue)
• Code Refactoring (internal change which is not user facing)
• Documentation
• Test, CI, or build

Component(s) if applicable

• BentoService (service definition, dependency management, API input/output adapters)
• Model Artifact (model serialization, multi-framework support)
• Model Server (mico-batching, dockerisation, logging, OpenAPI, instruments)
• YataiService gRPC server (model registry, cloud deployment automation)
• YataiService web server (nodejs HTTP server and web UI)
• Internal (BentoML's own configuration, logging, utility, exception handling)
• BentoML CLI

Checklist:

• My code follows the bentoml code style, both ./dev/format.sh and
  ./dev/lint.sh script have passed
  (instructions).
• My change reduces project test coverage and requires unit tests to be added
• I have added unit tests covering my code change
• My change requires a change to the documentation
• I have updated the documentation accordingly

[codecov]

Codecov Report

Merging #1044 into master will decrease coverage by 0.03%.
The diff coverage is 55.55%.

@@            Coverage Diff             @@
##           master    #1044      +/-   ##
==========================================
- Coverage   63.58%   63.54%   -0.04%     
==========================================
  Files         125      125              
  Lines        8262     8274      +12     
==========================================
+ Hits         5253     5258       +5     
- Misses       3009     3016       +7     

Impacted Files	Coverage Δ
bentoml/saved_bundle/loader.py	57.14% <55.55%> (-1.74%)	⬇️

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