{Packaging} Upgrade pip version in RPM

[finlaysawyer]

Description
Upgrade pip version to 21.0.1 in bundled Python to solve some extension install/usage issues like #16858

This PR continues on from the work done in #17091, also upgrading pip for RPM distros such as CentOS.

Testing Guide
Verify the new pip version by checking the installation: /usr/lib64/az/lib/python3.6/site-packages/pip-21.0.1.dist-info.
You can also verify the issue no longer exists by installing the azure-devops extension and using az devops login.

History Notes

[Component Name 1] BREAKING CHANGE: az command a: Make some customer-facing breaking change.
[Component Name 2] az command b: Add some customer-facing feature.

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[ghost]

Thank you for your contribution finlaysawyer! We will review the pull request and get back to you soon.

[yonzhan]

@jiasli for awareness

[fengzhou-msft]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 2 pipeline(s).

[fengzhou-msft]

@finlaysawyer thanks for the PR. I tested it and it works fine. I changed the title as RPM package is not using a bundled python but the system python with CLI's own site-packages.

The below az script used by RPM (which az |xargs cat to see the content) sets a PYTHONPATH when running CLI commands and therefore pip under /usr/lib64/az/lib/python3.6/site-packages will be loaded instead of the one in system /usr/lib/python3.6/site-packages. If you simply run /usr/bin/python3 -m pip -V, you should still see an old version from /usr/lib/python3.6/site-packages.

#!/usr/bin/env bash
AZ_INSTALLER=RPM PYTHONPATH=/usr/lib64/az/lib/python3.6/site-packages /usr/bin/python3 -sm azure.cli "$@"