Refactor sanity tests

[mreso]

Description

Refactored torchserve sanity tests as preparation for pytest integration
Fixes #(issue)

Type of change

Please delete options that are not relevant.

• Refactoring

Feature/Issue validation/testing

Please describe the Unit or Integration tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

• python torchserve_sanity.py

Checklist:

• Did you have fun?
• Has code been commented, particularly in hard-to-understand areas?

[codecov]

Codecov Report

Merging #2219 (59e1c4a) into master (d23d2ab) will not change coverage.
The diff coverage is n/a.

❗ Current head 59e1c4a differs from pull request most recent head 6bcf61f. Consider uploading reports for the commit 6bcf61f to get more accurate results

@@           Coverage Diff           @@
##           master    #2219   +/-   ##
=======================================
  Coverage   70.40%   70.40%           
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  Files          75       75           
  Lines        3392     3392           
  Branches       57       57           
=======================================
  Hits         2388     2388           
  Misses       1001     1001           
  Partials        3        3           

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