`kern.uuid` is misinterpreted as a machine ID when it's actually a kernel version identifier

[rpendleton]

The readPlatformMachineID function in hostid_darwin.go performs a syscall to obtain kern.uuid, and it uses the result as the machine ID. This value isn't actually meant to be a unique ID for a machine, but rather a unique ID for the currently running kernel version.

To verify this, you can run sysctl kern.uuid and then search for the value on Google, and as long as your current version of macOS has been released for a while, you'll likely find other people with the same ID.

(For concrete examples of this, see shirou/gopsutil#1058.)