Inform TopUser about GPFS being nearly full

The usage of the GPFS file system can be checked with the command:

erle1100@carl$ df -h $WORK
Filesystem      Size  Used Avail Use% Mounted on
gss             879T  831T   49T  95% /gss

The 25 top users can be identified with the command:

erle1100@carl$ cd ClusterScripts/diskusage/
erle1100@carl$ ./disk_usage.py --work -g -n 25 -s t -p
Directories:      'work'
abcd1234    (Jon Doe)                  agcomp1                        49.81
efgh5678    (Jane Doe)                 agcomp2                        27.78