Fix linting job for tools

[fdrozdowski]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build was run locally and any changes were pushed
• Lint has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

Linting jobs kicked off by GitHub actions use incorrect test directory in the tools package:
test/main/python. This results in failures of this kind:

  python -m flake8 test/main/python --max-line-length 88
  shell: /bin/bash -e {0}
  env:
    pythonLocation: /opt/hostedtoolcache/Python/2.7.18/x64
test/main/python:0:1: E902 IOError: [Errno 2] No such file or directory: 'test/main/python'
##[error]Process completed with exit code 1

see https://github.com/delphix/virtualization-sdk/pull/122/checks

What is the new behavior?

Fix the linting command to target the correct directory: src/test/python.

Does this introduce a breaking change?

• Yes
• No

Other information

[jeffngo]

LGTM