Upgrade SLES12 Test Server From SLES12_SP3 to SLES12_SP5

[steelhead31]

Issues are now occuring when trying to keep SLES12_SP3 up to date. It is now required to upgrade the SLES12 test server from SLES12_SP3 to SLES12_SP5 , so as to support the newer , more secure versions of SSL, particularly the TLS1.3 standard.

[sxa]

SLES12 system is currently disconnected due to too many issues on that version. We should look at whether we can continue to support this.

[sxa]

We have a docker container at test-docker-sles12-s390x-1 which is online and (presumably) usable. The physical machine test-marist-sles12-s390x-2 should potentially be decommissioned as it cannot easily be maintained. We do have a physical SLES15 system to test on non-containerised hardware.