Add defensive mitigation to prevent repeated guest-get-osinfo calls that
trigger buggy behavior in QEMU guest agent 9.0.2 on OpenBSD 7.6.
The issue: OpenBSD doesn't have /etc/os-release (Linux convention), and
qemu-ga 9.0.2 appears to spawn excessive helper processes trying to read
this file whenever guest-get-osinfo is called. These helpers don't clean
up properly, eventually exhausting the process table and crashing the VM.
The fix: Track consecutive OS info failures per VM. After 3 failures,
automatically skip future guest-get-osinfo calls for that VM while
continuing to fetch other guest agent data (network interfaces, version).
This prevents triggering the buggy code path while maintaining most guest
agent functionality.
The counter resets on success, so if the guest agent is upgraded or the
issue is resolved, Pulse will automatically resume OS info collection.
Related to #692
3e90737448