CP-43131: Make gvt-g support configurable

[liulinC]

This PR will not be merged until xs9 is ready,
Please just help to review this PR and approve if you are happy, we will merge it later.

Edit: This PR is updated to make gvt-g support configurable, so it can be merged to master as early as possible,
The legacy code can be removed later at proper time.

[johnelse]

So long, old friend 👋

[liulinC]

So long, old friend 👋

So long, old friend 😄

[robhoes]

@johnelse is still around and watching PRs here!!

[jonludlam]

Lots of us are still watching! 👀

[robhoes]

Oh dear... we'd better be more careful about what we are saying here... 😬

[liulinC]

I rebase to one single commit as the design now has been updated according to @edwintorok ,
We introduce configurable item, and drop/support this vGPU on demand.

[edwintorok]

I think the checks in start/resume/resume_on are redundant and would be covered by the 'allocate_vm_to_host' check.

What happens to the PGPUs though, will XAPI do the right thing on startup and remove the gvt-g ones if not supported due to the change in the 'find_or_create_supported'?

[liulinC]

I think the checks in start/resume/resume_on are redundant and would be covered by the 'allocate_vm_to_host' check.

What happens to the PGPUs though, will XAPI do the right thing on startup and remove the gvt-g ones if not supported due to the change in the 'find_or_create_supported'?

1. Indeed, all the three function will reach allocate_vm_to_host, but that is at very quick deep/later stage, with lots of xapi effort wasted, besides that, that happens when xapi to allocate a host to the VM, thus, the error message looks not straight forward,

# xe vm-start uuid=5e4ff268-c692-b202-6c23-8186266d59bd 
There are no suitable hosts to start this VM on.
The following table provides per-host reasons for why the VM could not be started:

    : Cannot start here [Server_error(VGPU_TYPE_NO_LONGER_SUPPORTED, [ Intel Corporation: Intel GVT-g ])]

With current early check and block,

# xe vm-start uuid=5e4ff268-c692-b202-6c23-8186266d59bd 
VGPU type is no longer supported
type: Intel Corporation: Intel GVT-g

I would like to argue just keep it (yes, we can handle the exception and re-raise at proper place, but that sounds more complicated.)

2. gvt-g is one type of vGPU, passthrough (intel gvt-d) can still work well.

[liulinC]

push -f just squash the history and rebase master before merge.