conf: added cf_warning API
log: update warnings to use cf_warning
log: warn on error retrieving auto value for NSID and identity
log: cache hostname lookup for nsid and identity
Merge branch 'conf-hostname-error' into 'master'

Config hostname errors

Included changes:

- log warnings properly
- issue warning when FQDN retrieval fails for system.identity and system.nsid
- cache hostname lookup

refs #306

See merge request !304