dashboard: subj_alt_names fact refactor

dashboard: subj_alt_names fact refactor

the current way the variable is built results in:

```
2021-08-03 04:18:23,020 - ceph.ceph - INFO - ok: [ceph-sangadi-4x-indpt6-node1-installer] => changed=false
  ansible_facts:
    subj_alt_names: |-
      subjectAltName=ceph-sangadi-4x-indpt6-node1-installer/subjectAltName=10.0.210.223/subjectAltName=ceph-sangadi-4x-indpt6-node1-installersubjectAltName=ceph-sangadi-4x-indpt6-node2/subjectAltName=10.0.210.252/subjectAltName=ceph-sangadi-4x-indpt6-node2/
```

which is incorrect.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1978869
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 6f1a0634f73ad1f41af613a9452dc9c5f70b2702)