* Always use /proc/sys/kernel/random/boot_id to confirm reboot on Linux
/proc/sys/kernel/random/boot_id is available since kernel 2.3.16 and
should be safe to rely on.
The previously used method by checking the system boot time using who -b
turned out to be unreliable: Some systems lacking an RTC report the Unix
epoch as boot time, but the code trying to detect that did't always
work.
Closes#46562
* Change DEFAULT_BOOT_TIME_COMMAND
- change to usinsg /proc by default
- add BOOT_TIME_COMMANDS for BSD, Solaris, and macOS
