[Documentation] Clarification on node selection parameters in USAGE.md

[Anish701]

Summary

USAGE.md mentions how tests can be configured using a combination of parameters. The host, job, and nodelabel parameters all involve node selection. To clarify behavior when multiple node selection parameters are used together, it would be helpful to mention that Autopilot runs the tests on nodes that match any of the specified parameters. In other words, Autopilot takes the set union rather than the set intersection.

Impact

Only the USAGE.md page will be updated. The following sentences will be added under the list of parameters:
Note that if multiple node selection parameters (host, job, nodelabel) are provided together, Autopilot will run tests on nodes that match any of the specified parameters (set union). For example, the following command will run the pciebw test on all nodes that either have the label label1 OR are running the job jobKey=job2 because both nodelabel and job parameters are provided in the input:
curl "http://<route-name>/status?check=pciebw&nodelabel=label1&job=default:jobKey=job2"

• _What pages will need to be updated? USAGE.md
• _Will there be broken links with these changes? No.
• _Are there any images you're adding or external content that exists outside the repository? No.