Update main.yml

Do consider shortening this temporary directory label

1) spank (Slurm Plug-in Architecture for Node/Job (K)control) has other customised functions beside creating private temp space for jobs, we might be using other spank plugins in the future

2)Having a shorten label, will improve readability during troubleshooting

3)Proposed structure will be:
/mnt/privatedir/
/mnt/privatedir/tmpdir.1.0
/mnt/privatedir/tmpdir.2.0
/mnt/privatedir/tmpdir.3.0
/mnt/privatedir/tmpdir.4.0
/mnt/privatedir/tmpdir.5.0
/mnt/privatedir/tmpdir.6.0
/mnt/privatedir/tmpdir.7.0