Fix Deployment Guide for kolla-kubernetes

In this doc :
https://docs.openstack.org/kolla-kubernetes/latest/deployment-guide.html

after step of deploy Kubernetes with kubeadm, the note is :

If the following issue occurs after running this command:

preflight] Some fatal errors occurred:
/proc/sys/net/bridge/bridge-nf-call-iptables contents are not set to 1

There are two work-arounds:
Add net.bridge.bridge-nf-call-ip6tables = 1 and
net.bridge.bridge-nf-call-iptables = 1 to /etc/sysctl.conf

Type sysctl -p to apply the settings from /etc/sysctl.conf
Type sysctl net.bridge.bridge-nf-call-ip[6]tables to
verify the values are set to 1.
-------------------------------------

Modify preflight] to [preflight].

Modify command 'sysctl net.bridge.bridge-nf-call-ip[6]tables' to
'sysctl net.bridge.bridge-nf-call-ip6tables' and
'sysctl net.bridge.bridge-nf-call-iptables'

Change-Id: Ib19ea6e6893967e99cd7f6f1b8c0b83a0f8088b5
Close-bug: #1707149

doc/source/deployment-guide.rst

@@ -218,7 +218,7 @@ Deploy Kubernetes with kubeadm::
 
    If the following issue occurs after running this command:
 
-   `preflight] Some fatal errors occurred:
+   `[preflight] Some fatal errors occurred:
    /proc/sys/net/bridge/bridge-nf-call-iptables contents are not set
    to 1`
 
@@ -228,8 +228,8 @@ Deploy Kubernetes with kubeadm::
      `net.bridge.bridge-nf-call-iptables = 1` to
      ``/etc/sysctl.conf``
    - Type `sysctl -p` to apply the settings from /etc/sysctl.conf
-   - Type `sysctl net.bridge.bridge-nf-call-ip[6]tables` to verify the
-     values are set to 1.
+   - Type `sysctl net.bridge.bridge-nf-call-ip6tables` and 
+     `sysctl net.bridge.bridge-nf-call-iptables` to verify the values are set to 1.
    - Or alternatively Run with `--skip-preflight-checks`. This runs
      the risk of missing other issues that may be flagged.