Improved Windows compatibility for machine command

[arixmkii]

Extracting more changes done during experiment in #13006 and continuation of #15372 (split into independent PRs as the first one is already reviewed and they are pretty independent).

It was checked to compile on MacOS and Windows and as it is purely refactoring, no behavior changes are expected.

List of changes

Fixing command line genarated

The only non platform specific change is

append(cmd, []string{"-qmp", monitor.Network + ":" + monitor.Address.GetPath() + ",server=on,wait=off"}...)

This is a correction, because Qemu is using unix: (also tcp: for TCP) not unix:/ to set the protocol. It was working before, because address is absolute and additional leading / is harmless).

Windows aware runtime directory

On windows the only option is to use either user specific or system wide AppData directories

Extracting unix specific parts from machine.go

Parts, which only can compile on unix are moved to _unix version and _windows alternatives (taking into account some limitations, because of lack of signaling) are provided.

Does this PR introduce a user-facing change?

None

[NO NEW TESTS NEEDED]

[arixmkii]

This doesn't enable Qemu for windows. So, no new functionality added and refactorings should be covered by existent tests, thus no tests provided for now.

[rhatdan]

@arixmkii Builds are failing, I added the [NO NEW TESTS NEEDED] flag.

[mheon]

/approve
@n1hility PTAL

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: arixmkii, mheon

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[n1hility]

I have some notes that I will paste shortly, and will post some thoughts on #13006

[n1hility]

Thanks for the update to the PR! I have one more follow-up.

[n1hility]

Also looks like some lingering compile issues

[arixmkii]

I believe a single failed test for rootless ubuntu could be just flaky one or a glitch.

[n1hility]

LGTM

I'll rerun the flake

[arixmkii]

@n1hility do you expect some more work with this one (like me rebasing it, etc)? It says it still is waiting for your approval.

[rhatdan]

/lgtm

[rhatdan]

Thanks @arixmkii