support: Change PYTHONCMD to python3

[tbunch1]

Make it so that python3 is used to run scripts.

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): [N/A]
• Platform(s): [N/A]
• Application(s): [N/A]

Additional configuration

None.

Description of changes

Change makefile.patch so that python3 is used to run Python scripts.
From what we could tell all other instances of python have been replaced by python3.

GitHub-Fixes: #1006

[nderjung]

Hi @tbunch1! Thanks for the contribution!

If you are co-authoring commits with peers, please include their sign-off as part of the commit message. Thanks!

[mariasfiraiala]

Thank you for the contribution @tbunch1! The changes look fine, however I have some comments regarding the commit message.

1. As @nderjung mentioned, you need to add the Co-authored-by tag inside the commit message. You have edited the PR message, not the commit message, so please do that.

2. Add a valid email to the Signed-off-by tag; <92049355+tbunch1@users.noreply.github.com> is automatically generated by GitHub so it doesn't reflect your real details (and it looks kinda bad).

That's all on my part, thanks!

[StefanJum]

Hi. The changes look good, but you all need to add a signed-off-by tag to the commit message.

[nderjung]

Hi, I think the multiple Co-authored-by is enough with at least 1 Signed-off-by by the committer. This PR is good to go imho. Thanks!

Reviewed-by: Alexander Jung alex@unikraft.io

[mariasfiraiala]

Looks good, thanks!

Reviewed-by: Maria Sfiraiala maria.sfiraiala@gmail.com

[StefanJum]

Reviewed-by: Stefan Jumarea stefanjumarea02@gmail.com