etcd join workflow fix when the first attempt fails

[makhov]

Description

Currently, if the first attempt to join etcd cluster fails (e.g. /v1beta1/etcd/members request returned 500), k0s won't try to join etcd again, because needToJoin() function only checks for the existence of the certificates.

This causes issues for k0smotron, where we spin up new machines in unpredictable order

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Checklist:

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[twz123]

Wondering if it's worth to add retries for 5xx errors to the etcd join process itself, too.

[k0s-bot]

Successfully created backport PR for release-1.28:

• [Backport release-1.28] etcd join workflow fix when the first attempt fails #4906

[k0s-bot]

Successfully created backport PR for release-1.29:

• [Backport release-1.29] etcd join workflow fix when the first attempt fails #4907

[k0s-bot]

Successfully created backport PR for release-1.30:

• [Backport release-1.30] etcd join workflow fix when the first attempt fails #4908

[makhov]

There are some retries, but they are too fast