Ensure kubeadm doesn't use proxy

[champtar]

*_proxy variables might be present in the environment (/etc/environment, bash profile, ...)
When this is the case we end up with those proxy configuration in /etc/kubernetes/manifests/kube-*.yaml manifests

We cannot unset env variables, but kubeadm is nice enough to ignore empty vars
https://github.com/kubernetes/kubernetes/blob/93d288e2a47fa6d497b50d37c8b3a04e91da4228/cmd/kubeadm/app/util/env.go#L27

What type of PR is this?
/kind bug

What this PR does / why we need it:

Which issue(s) this PR fixes:
Fixes #6250

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Fix issue when *_PROXY variables are present in the environment

[k8s-ci-robot]

Hi @champtar. Thanks for your PR.

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[floryut]

/ok-to-test

[michalskalski]

Shouldn't playbooks configure proper no_proxy on environment which would be inherited by kubeadm? For installation maybe that is ok to ignore proxy settings but for later use things like local kubectl shouldn't probably use proxy too.

[champtar]

Shouldn't playbooks configure proper no_proxy on environment which would be inherited by kubeadm? For installation maybe that is ok to ignore proxy settings but for later use things like local kubectl shouldn't probably use proxy too.

Problem is there are many ways to configure proxy on a system, this could be an option to put the computed values in /etc/environment, but for sure kubeadm should not have proxy set as it leads to issues. I can add this proxy_disable_env to all kubectl / calicoctl calls in this PR or in a follow up PR.

[champtar]

I can add this proxy_disable_env to all kubectl / calicoctl calls in this PR or in a follow up PR.
or not

$ git grep '/kubectl ' | wc -l
153
$ git grep 'kube:' | wc -l
76

[michalskalski]

Actually I thought more about situation after deployment, in environment with http proxy there will be environment variables exported for example with /etc/environment. If no_proxy variable will not be extended with k8s addresses then kubectl may try connect through proxy which probably will not be desired behavior. Even for installation, if playbook would set no_proxy variable in /etc/environment with values which are already calculated then that could be inherited by commands executed later.

[champtar]

Proxies are a mess :(
Setting the values computed by kubespray in /etc/environment might not be 100% reliable (see #6250, some people are using profile.d) so I'm trying to think a bit more about it.

[floryut]

/cc @EppO
/cc @oomichi

[oomichi]

Nice work.

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: champtar, floryut

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