Don't fail if a service name cannot be looked up in LDAP

[rcritten]

A new method was introduced to handle more IPA services. This requires looking some of them up in LDAP. dirsrv not running was not being caught so raised an error instead.

Fixes: #312

[flo-renaud]

Hi @rcritten
Thanks for the PR, works for me. Tested on fedora 39:

# systemctl stop [email protected]
# ipa-healthcheck --source ipahealthcheck.ipa.topology
Source 'ipahealthcheck.ipa.topology' is missing one or more requirements 'dirsrv'
# ipa-healthcheck --source ipahealthcheck.meta --check krb5kdc
Source 'ipahealthcheck.meta' is missing one or more requirements 'dirsrv'
# ipa-healthcheck
[
  {
    "source": "ipahealthcheck.meta.services",
    "check": "dirsrv",
    "result": "ERROR",
    "uuid": "dd8f25d7-6791-46ce-9a11-c60d2f4683e3",
    "when": "20231114084138Z",
    "duration": "0.008669",
    "kw": {
      "status": false,
      "msg": "dirsrv: not running"
    }
  }
]
#