[utils] Rewrite slurm.pl from scratch

The new file calls sbatch passing the batch file on stdin, and
waits for completion of the script without polling, rather by
passing the --wait switch to sbatch.

Slurm has a hardcoded polling schedule for waiting. Specifically,
it checks if the job has completed for 2s, then increases the
wait time by 2s until it maxes out at 10s. Because of this, even
very short Kaldi batches often incur extra 5s wait delays on
average. The following patch reduces the poll time to 1s without
growth:

https://github.com/burrmill/burrmill/blob/v0.5-beta.2/lib/build/slurm/sbatch.19.patch

It has been tested to apply cleanly up until Slurm v20.1, and is
unlikely to break in future. Please open a ticket in the
https://github.com/burrmill/burrmill repository if your Slurm
source does not patch.

You do not need administrative access to the cluster; you can just
build your own version of sbatch and place on the PATH. Internally
it uses only Slurm RPC calls, and does not require many dependencies.

Author: kkm000