Fixes the reboot/fast-reboot command args validation and gets the user confirmation before reboot.

[Kalimuthu-Velappan]

- What I did

Fixes the reboot/fast-reboot command args validation and gets the user confirmation before the system reboot:

Reboot command takes all types of arguments and doesn't do any argument validation. Reboot command is a sensitive command and it may cause loss of unsaved data if the command is given accidentally. So, to avoid the accidental issue of reboot command, user confirmation is added before the system reboot.

    root@sonic:/home/admin# reboot
    Warning: This command would cause the switch to reboot
    and result in traffic disruption.
    Are you sure you want to reboot? [y/N]
    ....

New option '-y' is added to skip the user configuration.

This change might impact the automation scripts. It is recommended to use the below logic in the automation script to support both the varients of reboot command.

      if (reboot -h |grep “skip the user confirmation”) is present
             reboot -y
      else
             reboot

- How I did it

The following changes are done in both reboot and fast-reboot commands.

• Added command line args validation
• Added support to perform the user confirmation before the system reboot
• Added a new option "-y" to skip user confirmation on both the reboot commands
• Added a new option "-f" to preform the force/quick reboot.

- How to verify it

1. Check the reboot command with user confirmation
   root@sonic:/home/admin# reboot
   Warning: This command would cause the switch to reboot
   and result in traffic disruption.
   Are you sure you want to reboot? [y/N]

    root@sonic:/home/admin# fast-reboot
    Are you sure you want to reboot? [y/N]
   

2. Check the reboot command to skip the user confirmation
   root@sonic:/home/admin# reboot -y
   ...

    root@sonic:/home/admin# fast-reboot -y
    ...
   

3. Verify the invalid command-line options
   root@sonic:/home/admin# reboot junk
   Unsupported reboot option
   Usage /usr/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
            -y     : skip the user confirmation
            -f     : force reboot
   

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

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

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