XSI-1969 XSI-1973 use https for localhost migration

[lindig]

We observe an instability of localhost migration with NVidia SRIOV GPUs since we starting to fall back to http (rather than https) for localhost migration. Outside of development, localhost migration is used during device model restart.

Use HTTPS for localhost migration. This seems to improve stability (but is not the root cause).

[robhoes]

I can't see why HTTPS within a host would be useful, while it will affect performance. And this change will affect performance (and potentially stability) for many more use cases than vGPU localhost migration. So I am not in favour of this unless we really understand why it is better and there is no alternative.

[edwintorok]

Can we make it configurable via xapi.conf instead? That'd still allow us to test https on vs off to identify what the root cause is, but without having to bisect builds: we could do this test using the same (latest) build, by tweaking this parameter on/off.

[lindig]

This is purely on the observation that it appears to be more stable but it is not addressing a root problem. Localhost migration is not a typical use case but it failing is a problem - so I think we should do this if it improves the stability. @edwintorok the flag from xapi.conf still has an effect: migration-https-only = false forces to use HTTP.

[freddy77]

It looks like an indication there's a race condition doing the migration that goes away due to time changes.
Not saying the workaround is not worth.

[robhoes]

so I think we should do this if it improves the stability

If I recall correctly, the change to not use HTTPS for localhost connections was also to improve stability. Also, this change affects all VMs, not just those with vGPUs

[lindig]

We could limit this to VMs with vGPU. But there is a cost: all these if-then-else mazes create untested areas.