Remove annoying warnings

Those warnings don't have any specail meaning and usage.
Resolve #825.

cdist/util/ipaddr.py

@@ -45,8 +45,6 @@ def resolve_target_host_name(host, family=0):
         log.debug("derived host_name for host \"{}\": {}".format(
             host, host_name))
     except (socket.gaierror, socket.herror) as e:
-        log.warning("Could not derive host_name for {}"
-                    ", $host_name will be empty. Error is: {}".format(host, e))
         # in case of error provide empty value
         host_name = ''
     return host_name
@@ -59,8 +57,6 @@ def resolve_target_fqdn(host):
         log.debug("derived host_fqdn for host \"{}\": {}".format(
             host, host_fqdn))
     except socket.herror as e:
-        log.warning("Could not derive host_fqdn for {}"
-                    ", $host_fqdn will be empty. Error is: {}".format(host, e))
         # in case of error provide empty value
         host_fqdn = ''
     return host_fqdn