MXS-1660 Turn client hostname lookup failure into a warning

This is used only in case of everything else fails and this lookup
is not unlikely to fail if the client comes from some machine on
an internal network.

server/modules/authenticator/MySQLAuth/dbusers.c

@@ -701,8 +701,8 @@ static bool get_hostname(DCB *dcb, char *client_hostname, size_t size)
 
     if (lookup_result != 0)
     {
-        MXS_ERROR("Client hostname lookup failed, getnameinfo() returned: '%s'.",
-                  gai_strerror(lookup_result));
+        MXS_WARNING("Client hostname lookup of '%s' failed, getnameinfo() returned: '%s'.",
+                    client_hostname, gai_strerror(lookup_result));
     }
     else
     {