balloons: add support for isolated cpus.

[fmuyassarov]

The isolcpus boot parameter allows you to isolate specific CPUs from
the general SMP balancing and scheduler algorithms. Currently, when a
balloon picks up CPUs, it does not differentiate between isolated and
non-isolated CPUs. This change improves the balloon's logic to:

1. Distinguish between isolated and non-isolated CPUs.
2. Allow users to preferably select isolated CPUs, though this is not guaranteed.
3. Avoid using isolated CPUs unless specifically requested by the user via CR.

[klihub]

Once all review comments are addressed I'm happy with this as soon as @askervin finds it good to go in.

[askervin]

Nit: spotted a typo in documentation.

[klihub]

I have a number of new review comments and suggestions related to the e2e test framework additions and the test scriptlet itself.

[klihub]

LGTM.

A few more nits...

[askervin]

After passed test pod0 is left behind:

vagrant@n4c16-generic-ubuntu2204-containerd:~$ kubectl get pods -A
NAMESPACE     NAME                                                          READY   STATUS    RESTARTS      AGE
default       pod0                                                          2/2     Running   2 (92s ago)   2m10s
...

@klihub already suggested changes to cleanup() so that nothing is left behind if the test passed.

[fmuyassarov]

After passed test pod0 is left behind:

vagrant@n4c16-generic-ubuntu2204-containerd:~$ kubectl get pods -A
NAMESPACE     NAME                                                          READY   STATUS    RESTARTS      AGE
default       pod0                                                          2/2     Running   2 (92s ago)   2m10s
...

@klihub already suggested changes to cleanup() so that nothing is left behind if the test passed.

@askervin @klihub this should be addressed now. PTAL.

[askervin]

There seems to be a risk of failing next tests if this passes.

[askervin]

LGTM. Thanks for this new feature, @fmuyassarov!