Use new sysctl method

First, thanks for writing this, this is a great resource.  Many guides use scripts to do everything and this doesn't.

For "Enable IP_Forwarding" section, a cleaner method would be to use the sysctl.d directory so no files are modified:

echo "net.ipv4.ip_forward=1" > /etc/sysctl.d/99-openstack-ipv4-forwarding.conf
service procps start