Add macOS VM support to the vmtest framework using Tart's pre-built
macOS images (ghcr.io/cirruslabs/macos-tahoe-base) instead of building
from IPSW. The Tart image has SIP disabled and SSH enabled.
At test time, the Tart base image's disk, NVRAM, and hardware identity
are APFS-cloned into a tailmac-compatible directory layout, and the VM
is booted headlessly via tailmac's Host.app (Virtualization.framework)
with its NIC connected to vnet's dgram socket.
New features:
- tailmac.go: ensureTartImage (auto-pull), cloneTartToTailmac (format
conversion), startTailMacVM (launch + cleanup)
- NoAgent() node option for VMs without TTA installed
- LANPing() for ICMP reachability testing via TTA's /ping endpoint
- IsMacOS field on OSImage, with GOOS/GOARCH support
- Dgram socket listener in Start() for macOS VMs
- Fix ReadFromUnix error spam on dgram socket close in vnet
TestMacOSAndLinuxCanPing verifies a macOS Tart VM and a gokrazy Linux
VM can ping each other on the same vnet LAN.
Updates #13038
Change-Id: I5e73a27878abf009f780fdf11a346fc857711cff
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>