reboot mechanism enhanced with reboot cause

[shyam77git]

What I did

• Prior to this change, reboot script is only externally trigged where reboot cause is always fixed i.e. (default's to 'user issued reboot command')
• In this PR (changeset), SONiC reboot is enhanced to accept reboot cause (reason) as an optional argument
• This enhancement enables system applications' (e.g. Fault detector/producer, Fault Manager/Handler) to pass reboot cause as an argument while initiating (system level) reboot
• This reboot cause in turn is saved to REBOOT_CAUSE_FILE for tracking and debugging purposes

How I did it

• Facilitated passing of a new optional argument (-r) to reboot command and handled it in reboot script
• For further details, refer to the 'Files changed' tab

How to verify it

Refer to UT scenarios and logs:
UT-reboot.txt

root@sonic:/home/cisco# reboot -h
Usage /usr/local/bin/reboot [options]
Request rebooting the device. Invoke platform-specific tool when available.
This script will shutdown syncd before rebooting.

Available options:
    -h, -? : getting this help
    -f     : execute reboot force
    -r     : specify reboot cause (reason) string in quotes

root@sonic:/home/cisco#

root@sonic:/home/cisco# reboot -r "rebooting due to xyz reason"
reboot_cause: rebooting due to xyz reason
requested COLD shutdown
/var/log: 0 B (0 bytes) trimmed on /dev/loop1
/host: 204.6 MiB (214548480 bytes) trimmed on /dev/sda3
Tue 06 Feb 2024 06:20:22 AM UTC Issuing OS-level reboot ...
Going to issue reboot command...
reboot cause specified
root@sonic:/home/cisco#

root@sonic:/home/cisco# show reboot-cause history
Name Cause

---

2024_02_06_06_23_30 System triggered reboot. reason: 'rebooting due to xyz reason' [User: system, Time: Tue 06 Feb 2024 06:20:13 AM UTC]
2024_02_06_01_07_29 reboot Tue 06 Feb 2024 01:04:43 AM UTC

Previous command output (if the output of a command-line utility has changed)

root@sonic:/home/cisco# reboot
requested COLD shutdown
/var/log: 0 B (0 bytes) trimmed on /dev/loop1
/host: 204.6 MiB (214548480 bytes) trimmed on /dev/sda3
Tue 06 Feb 2024 06:20:22 AM UTC Issuing OS-level reboot ...
root@sonic:/home/cisco#

New command output (if the output of a command-line utility has changed)

Note: Above-mentioned default 'reboot' command is kept intact.

Additional (optional) argument -r, if passed to the reboot, would have following outcome:
root@sonic:/home/cisco# reboot -r "rebooting due to xyz reason"
reboot_cause: rebooting due to xyz reason
requested COLD shutdown
/var/log: 0 B (0 bytes) trimmed on /dev/loop1
/host: 204.6 MiB (214548480 bytes) trimmed on /dev/sda3
Tue 06 Feb 2024 06:20:22 AM UTC Issuing OS-level reboot ...
Going to issue reboot command...
reboot cause specified
root@sonic:/home/cisco#

[shyam77git]

UT test scenario and logs:
UT-reboot.txt

[amulyan7]

LGTM