Need some improvement for the neutron configuration in install-guide

[Haomeng,Wang]

In install-guide.html "Configure Neutron to communicate with the Bare Metal Server" section, for the configuration as below:

[ovs]
network_vlan_ranges = physnet1
bridge_mappings = physnet1:br-eth2

We can not assume it should be configured in /etc/neutron/plugins/ml2/ml2_conf.ini, depends on the which config-file used for neutron-openvswitch-agent process, some time it is not /etc/neutron/plugins/ml2/ml2_conf.ini but /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini.

So if neutron-openvswitch-agent run with ovs_neutron_plugin.ini as the input config-file, we have to edit ovs_neutron_plugin.ini. to add the [ovs] section to enable the bridge mappings configuration.

And, the network_vlan_ranges options is not required for neutron flat network, the line can be removed from the guide.

[Haomeng,Wang (whaom)]

The result should be:

[root@localhost install]# ovs-vsctl show
80f45ddb-bdee-4a19-b2df-5df2a818b835
    Bridge br-int
        fail_mode: secure
        Port "int-br-eth1"
            Interface "int-br-eth1"
                type: patch
                options: {peer="phy-br-eth1"}
        Port br-int
            Interface br-int
                type: internal
    Bridge "br-eth1"
        Port "phy-br-eth1"
            Interface "phy-br-eth1"
                type: patch
                options: {peer="int-br-eth1"}
        Port "eth1"
            Interface "eth1"
        Port "br-eth1"
            Interface "br-eth1"
                type: internal
    ovs_version: "2.3.0"

[Haomeng,Wang (whaom)]

Fixed via https://review.openstack.org/#/c/143349/