[Enhance] Support CPU-only train and test in slurm cluster (#189)

[GhaSiKey]

Motivation

Support CPU-only train and test in slurm cluster. (#189)

Modification

Modify slurm check conditions to "flag = partition is not None"

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[ice-tong]

The commands of slurm launch also should be updated if cpu-only~

mim/mim/commands/train.py

Lines 252 to 257 in ff137cc

	cmd = [
	'srun', '-p', f'{partition}', f'--gres=gpu:{gpus_per_node}',
	f'--ntasks={gpus}', f'--ntasks-per-node={gpus_per_node}',
	f'--cpus-per-task={cpus_per_task}', '--kill-on-bad-exit=1'
	] + parsed_srun_args + [PYTHON, '-u', train_script, config
	] + common_args

[ice-tong]

The gridsearch command also need update~

mim/mim/commands/gridsearch.py

Lines 203 to 208 in ff137cc

	if launcher == 'slurm':
	msg = ('If launcher is slurm, '
	'gpus-per-node and partition should not be None')
	flag = (gpus_per_node is not None) and (partition is not None)
	if not flag:
	raise AssertionError(highlighted_error(msg))

[ice-tong]

Suggested change

	if gpus:
	if gpus_per_node:

[ice-tong]

Suggested change

	if gpus:
	if gpus_per_node:

[ice-tong]

Suggested change

	if gpus:
	if gpus_per_node:

[ice-tong]

Close due to the slurm can't launch without gpus, feel free to reopen if you have any question~