Modifing stack softlimit

Hi,
I've noticed cyclecloud recently changed the behavior for limits of stack sizes.
Now it add this:
```
$ cat /etc/security/limits.conf |grep stack
# - stack - max stack size (KB)
* hard stack unlimited
* soft stack unlimited
```
However I am not sure where this comes from, I can't find it in this repo and it is not from the CentOS HPC Image as far as I could tell (https://github.com/openlogic/AzureBuildCentOS)

In any case if someone else is falling over this, Abaqus at least does not accept unlimited as a soft limit.

Greetings
Klaas