Fix hostresolver setting for VZ, but disable it by default

[jandubois]

Since it was implicitly disabled for VZ, we cannot simply fix the bug, but change the default to match the previous de-facto default.

This PR now disables HostResolver by default, except for QEMU.

This implements option (1) from #4089.

[jandubois]

I believe this PR is working correctly.

Unfortunately it didn't help in tracking down the DNS issue with VZ¹ because it seems to happen with both HostResolver and with the gvisor-tap-vsock resolver, but that is a separate problem.

Footnotes

1. It is a relatively obscure failure that happens in CoreDNS when using kind with a usernet network while host.docker.internal is defined to point to host.lima.internal. It doesn't happen with QEMU, so maybe a bug in gvisor-tap-vsock, but still not clear. ↩

[jandubois]

It is suspicious that the QEMU integration test with the user-v2 network keeps failing.

It does pass for me locally, fwiw.

[AkihiroSuda]

  ==> /home/runner/.lima/net-user-v2/serial.log <==
  [  387.917819] cloud-init[1040]:   libsubid4 uidmap
  [  417.955457] cloud-init[1040]: 0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
  [  417.958231] cloud-init[1040]: Need to get 49.4 kB of archives.
  [  417.959752] cloud-init[1040]: After this operation, 208 kB of additional disk space will be used.
  [  417.961866] cloud-init[1040]: Ign:1 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 libsubid4 amd64 1:4.13+dfsg1-4ubuntu3.2
  [  447.985053] cloud-init[1040]: Ign:2 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 uidmap amd64 1:4.13+dfsg1-4ubuntu3.2
  [  478.020751] cloud-init[1040]: Ign:1 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 libsubid4 amd64 1:4.13+dfsg1-4ubuntu3.2
  [  508.049158] cloud-init[1040]: Ign:2 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 uidmap amd64 1:4.13+dfsg1-4ubuntu3.2
  [  538.083405] cloud-init[1040]: Ign:1 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 libsubid4 amd64 1:4.13+dfsg1-4ubuntu3.2
  [  568.115833] cloud-init[1040]: Ign:2 http://archive.ubuntu.com/ubuntu noble-updates/main amd64 uidmap amd64 1:4.13+dfsg1-4ubuntu3.2

https://github.com/lima-vm/lima/actions/runs/18024105718/job/51444457681?pr=4090

[jandubois]

It does pass for me locally, fwiw.

I can reproduce the problem even on macOS when explicitly asking for qemu:

limactl start -y --vm-type qemu ./hack/test-templates/net-user-v2.yaml

It seems like usernet configuration is different between QEMU and VZ.