Checking /sys/block to find scheduler(s). Issues 1276, 1325

[xnoguer]

Pull request that fixes issues 1325 and 1276. It checks /sys/block/*/queue/scheduler, and sets LINUX_KERNEL_IOSCHED with the scheduler of the last block device checked. A few observations:

• Was tested in Debian 11. Including a machine with more than one block device.
• It sets LINUX_KERNEL_IOSCHED with the scheduler of the last block device checked. I don't see Lynis does anything with this value later on (linux_kernel_io_scheduler in lynis-report.dat), so I don't know what would be done with more than one value for the scheduler (different scheduler for different devices).
• I recommend to ignore/hide whitespace when reviewing the changes in code.
• When testing behaviour for different schedulers this can be useful:
  xnoguer@ip:$ cat /sys/block/xvda/queue/scheduler
  mq-deadline [kyber] none
  xnoguer@ip:$
  xnoguer@ip:$ sudo echo "deadline" | sudo tee /sys/block/xvda/queue/scheduler
  deadline
  xnoguer@ip:$ cat /sys/block/xvda/queue/scheduler
  [mq-deadline] kyber none