Merge branch 'selftests-vsock-support-nested-vm-runner-for-vmtest-sh'

Bobby Eshleman says:

====================
selftests/vsock: support nested VM runner for vmtest.sh

This series fixes a few issues trying to launch vmtest.sh in a nested VM
environment and were discovered when trying to prepare the tests for
netdev CI/CD.

When taken together these patches make vmtest.sh work both on bare metal
and in nested VMs, regardless of the outer VM's user, coincidental path
overlaps, or filesystem settings.
====================

Link: https://patch.msgid.link/20260317-vsock-vmtest-nested-fixes-v2-0-0b3f53b80a0f@meta.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>