virt-host-validate: Fix error level for user namespace check

From the code it seems to me that we need user namespace if
configured in domain XML. Otherwise we don't use it at all.
However our tool is more strict about that. Fix this discrepancy.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

tools/virt-host-validate-lxc.c

@@ -59,7 +59,7 @@ int virHostValidateLXC(void)
         ret = -1;
 
     if (virHostValidateNamespace("LXC", "user",
-                                 VIR_HOST_VALIDATE_FAIL,
+                                 VIR_HOST_VALIDATE_WARN,
                                  _("User namespace support is recommended")) < 0)
         ret = -1;