Move job_name handling down alongside similar code in _opt_verify().

Move setting of SLURM_EXPORT_ENV in sbatch to _opt_verify().

Note some structural work to support this: add a new _env_early_opt()
to parse out key early environment variables, so that xlate_batch_script()
is no longer directly parsing the cli arguments or looking directly
for SBATCH_IGNORE_PBS in the environment.

Handle conversion to minutes here, and drop the ckpt_interval_str variables
from sbatch_opt_t and srun_opt_t.

Set as no_argument instead of optional_argument.

Move ifname to slurm_opt_t, rather than keeping it in sbatch_opt_t
and srun_opt_t, making the arg handling code much simpler.

Skip setting it to /dev/null as part of the reset, and move that logic
to _opt_verify().

Fix a mistake in the API in slurm_get_job_stdin() where StdIn= is
prepended to /dev/null if ifname == NULL.

Move efname to slurm_opt_t, rather than keeping it in sbatch_opt_t
and srun_opt_t, making the arg handling code much simpler.

Since 'sleep' is what will be executed, the correct JobName is sleep.

For sbatch - first_pass() is an explicitly separate phase, and will
clear the struct for us. Every successive call should feed in 'false'
to prevent sbatch_early_pass settings - like quiet / verbose - from
getting overwritten.

And some further cleanup now that all option parsing code is moved to
slurm_opt.c.

Move all logic for setting defaults and setting the name across
HetJob components in to _match_job_name().

Remove JOB_SALLOC_FLAG, and default_job_name from salloc_opt_t.

Just check if sentinel value of NO_VAL is still set instead.

Just check if sentinel value of NO_VAL is still set instead.

While here, drop test on SLURM_STARTED_STEP envvar which is never
set (was used with POE), and move this logic to _opt_verify().

Note that sbatch intentionally handles this in a different way -
it injects the file contents into the job script, rather than
sending it in burst_buffer in job_desc_msg_t.

Replace three implementations of _read_file() with create_mmap_buf().

Use _unknown_ as the name here, since ? is obviously invalid.

Drop egid from slurm_opt_t in favor of simpler handling of gid itself.

Drop euid from slurm_opt_t in favor of simpler handling of uid itself.

Note symbol hack to permit the help() functions to stay in place within
the commands for now.

Drop -u as an option for salloc/sbatch, since srun has it for --unbuffered.

Note symbol hack to permit the usage() functions to stay in place within
the commands for now.