Rewrite cert sync to use comm, not diff (#146)

[kyl191]

Rewrite the cert sync detection:

• overly reliant on magic paths (/tmp/existing-certs, etc)
• not cleaning up temp files
• empty files might be causing diff/grep/awk pipeline to error out (#146)

Changes:

• tempfile module used & cleaning up the generated tempfiles
• client list still written to disk, but use the ansible internal sort first so there's no additional call
• task file name changed from common.yml to more specific cert_sync_detection.yml
• simplified the existing cert check pipeline with globs

[kyl191]

Decent cleanup of the cert sync & revocation tasks.

Ran fine on a new centos 8 VM.

...
TASK [kyl191.openvpn : [cert sync] Create temporary file for existing certs] ***********************************************
changed: [129.146.168.176]
TASK [kyl191.openvpn : [cert sync] Create temporary file for expected certs] ***********************************************
changed: [129.146.168.176]
TASK [kyl191.openvpn : [cert sync] Write expected client list to temp file for comparison with existing certs] *************
changed: [129.146.168.176]
TASK [kyl191.openvpn : [cert sync] Get existing certs] *********************************************************************
changed: [129.146.168.176]
TASK [kyl191.openvpn : [cert sync] Find certs that exist but aren't supposed to (on disk, but not in client list)] *********
changed: [129.146.168.176]
TASK [kyl191.openvpn : [cert sync] Debug: Certs to revoke (skipped if none)] ***********************************************
ok: [129.146.168.176] => {
    "changed": false,
    "msg": "Will revoke additional certs: x230"
}
TASK [kyl191.openvpn : [cert sync] Cleanup temp files] *********************************************************************
changed: [129.146.168.176] => (item=/tmp/ansible.wtdse9j2temp)
changed: [129.146.168.176] => (item=/tmp/ansible.nvvhot9dtemp)
...
PLAY RECAP *****************************************************************************************************************
129.146.168.176            : ok=65   changed=15   unreachable=0    failed=0    skipped=53   rescued=0    ignored=0