Add configuration of ohcp-release and powertools into role

[sjpb]

Removes the need for users of this role to configure two aspects outside of the role:

• Installs an ohpc-release repo (see #6), appropriate for the Centos version (but if one's already present in the image, it won't try to change it)
• Enables PowerTools repo on Centos8 (see #41)

Given these changes it also adds a test on centos 8. Currently centos8 test fails on travis as ohpc-release repo fails GPG key check, however tests directly on molecule (using same image!) run as follows:

git checkout auto-centos8
git pull
MOLECULE_IMAGE=centos:7 molecule test --all # PASSES
MOLECULE_IMAGE=centos:8 molecule test --all # PASSES

(the commits on this are messy due to a failed rebase onto master but the diff looks good).

[jovial]

Probably worth squashing this one down?

[sjpb]

Centos 8 checks failing on molecule with

fatal: [testohpc-compute-1]: FAILED! => {"changed": true, "cmd": ["dnf", "config-manager", "--set-enabled", "PowerTools"], "delta": "0:00:00.232796", "end": "2020-11-05 19:13:36.545797", "msg": "non-zero return code", "rc": 1, "start": "2020-11-05 19:13:36.313001", "stderr": "No such command: config-manager. Please use /usr/bin/dnf --help\nIt could be a DNF plugin command, try: \"dnf install 'dnf-command(config-manager)'\"", "stderr_lines": ["No such command: config-manager. Please use /usr/bin/dnf --help", "It could be a DNF plugin command, try: \"dnf install 'dnf-command(config-manager)'\""], "stdout": "", "stdout_lines": []}

ETA: but work manually outside of molecule/docker

[sjpb]

Centos 8 checks failing on molecule with

fatal: [testohpc-compute-1]: FAILED! => {"changed": true, "cmd": ["dnf", "config-manager", "--set-enabled", "PowerTools"], "delta": "0:00:00.232796", "end": "2020-11-05 19:13:36.545797", "msg": "non-zero return code", "rc": 1, "start": "2020-11-05 19:13:36.313001", "stderr": "No such command: config-manager. Please use /usr/bin/dnf --help\nIt could be a DNF plugin command, try: \"dnf install 'dnf-command(config-manager)'\"", "stderr_lines": ["No such command: config-manager. Please use /usr/bin/dnf --help", "It could be a DNF plugin command, try: \"dnf install 'dnf-command(config-manager)'\""], "stdout": "", "stdout_lines": []}

ETA: but work manually outside of molecule/docker

Fixed by 56af43a