iSCSI: add support for scst

[chrboe]

Add scst (https://github.com/SCST-project/scst/) as a new supported implementation to the iSCSITarget and iSCSILogicalUnit resource agents.

All basic functionality that is supported by the other implementations is supported by scst as well.

[knet-jenkins[bot]]

Can one of the admins check and authorise this run please: https://ci.kronosnet.org/job/resource-agents/job/resource-agents-pipeline/job/PR-1890/1/input

[knet-jenkins[bot]]

Can one of the admins check and authorise this run please: https://ci.kronosnet.org/job/resource-agents/job/resource-agents-pipeline/job/PR-1890/2/input

[knet-jenkins[bot]]

Can one of the admins check and authorise this run please: https://ci.kronosnet.org/job/resource-agents/job/resource-agents-pipeline/job/PR-1890/3/input

[oalbrigt]

Thanks.