pip: 20.3.4 -> 21.0.1

[groodt]

Note: No urgency to rush this. It introduces a breaking change where pip_install will only work for Python3+. If any release of rules_python needs to be done prior to prepare a final Python2 compatible release, it should be done before merging this.

PR Checklist

Please check if your PR fulfills the following requirements:

• Does not include precompiled binaries, eg. .par files. See CONTRIBUTING.md for info
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Follow up to #405

This PR introduces pip 21.0.1 as the vendored version of pip. This version of pip will only support Python 3+ and is pip breaking away from Python 2 support since pip 21.0: https://pip.pypa.io/en/stable/news/#id1

My suggestion would be to first merge #405 and prepare a release or tag along with documentation around the pip_install Python 2 support. Then this PR can be rebased against upstream bazelbuild/rules_python and merged to support Python 3 pip_jnstall support only for future development.

Does this PR introduce a breaking change?

• Yes
• No

Other information

PR Checklist

Please check if your PR fulfills the following requirements:

• Does not include precompiled binaries, eg. .par files. See CONTRIBUTING.md for info
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Follow up to #405

This PR introduces pip 21.0.1 as the vendored version of pip. This version of pip will only support Python 3+ and is pip breaking away from Python 2 support since pip 21.0: https://pip.pypa.io/en/stable/news/#id1

My suggestion would be to first merge #405 and prepare a release or tag along with documentation around the pip_install Python 2 support. Then this PR can be rebased against upstream bazelbuild/rules_python and merged to support Python 3 pip_jnstall support only for future development.

Does this PR introduce a breaking change?

• Yes
• No

Python3 only support for pip_install due to pip upgrade.

[groodt]

Build failure is due to CI running Python3.5 which is EOL.

pip 21.x dropped support for all Python 2 and Python 3.5.