✨ Add sentinel file to signal successful bootstrapping

[CecileRobertMichon]

What this PR does / why we need it: This PR does three things:

1. Add the presence of /run/cluster-api/bootstrap-success.complete to signal successful completion of bootstrapping to the Bootstrap Provider contract.
2. Adds commands to write the sentinel file when kubeadm init and kubeadm join succeed to CABPK. This is done in a way that works for both Linux and Windows machines.
3. Implements the bootstrap file check and condition for the Docker provider

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #3716

[CecileRobertMichon]

/cc @jsturtevant @jdef

[k8s-ci-robot]

@CecileRobertMichon: GitHub didn't allow me to request PR reviews from the following users: jdef.

Note that only kubernetes-sigs members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

/cc @jsturtevant @jdef

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[CecileRobertMichon]

docker e2e is failing because the docker provider is modifying runcmd to append --ignore-preflight-errors=all... will fix on Monday

[CecileRobertMichon]

/retest

[fabriziopandini]

/milestone v0.4.0

[CecileRobertMichon]

/hold

trying to add a test

[jdef]

/lgtm

[k8s-ci-robot]

@jdef: changing LGTM is restricted to collaborators

In response to this:

/lgtm

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[jdef]

To ensure that this is working as expected, maybe integration testing looks something like:

1. Add a postKubeadmCommands entry (for either the KCP or non-KCP docker example) that asserts the presence of the sentinel file; a failure can be signaled .. somehow :)
2. Add a test case that injects an (optional) "poison pill" to the docker infra, such that "kubeadm init" (or join) fails, and in such case, assert that the sentinel file is not created.

My hunch is that the 2nd case is a bit more work, but it also tests the logic for "ONLY create the sentinel if kubeadm succeeds".

Failure signal probably needs some thought. Straw man: a polling mechanism in docker/docker/machine.go::ExecBootstrap that waits X time for the sentinel file to appear in the container (since kubeadm has already finished executing (or failing) the wait time can probably be short).

[CecileRobertMichon]

/hold cancel

[vincepri]

/lgtm

[CecileRobertMichon]

/assign @fabriziopandini

[fabriziopandini]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: fabriziopandini

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [fabriziopandini]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment