[integ-tests-framework] Use Lazy import of dependencies in reports_generator

[hanwen-cluster]

Description of changes

Sometimes, only a few functions in reports_generator.py are called by a environment, which doesn't have to have all Python dependencies installed

Tests

• test will run after the PR is merge

Checklist

• Make sure you are pointing to the right branch.
• If you're creating a patch for a branch other than develop add the branch name as prefix in the PR title (e.g. [release-3.6]).
• Check all commits' messages are clear, describing what and why vs how.
• Make sure to have added unit tests or integration tests to cover the new/modified code.
• Check if documentation is impacted by this change.

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[gmarciani]

This is a short term solution to prevent alarms.
The long term solution is to remove the dependency on SUPPORTED_OS constant and install pandas and other dependencies in Jenkins.