Brush up Quantum part of basic install guide

* Controller node
  * Add Horizon (Dashboard) URL in Dashboard Installation section
  * Correct the output of "glance image-list"
  * Remove Open vSwitch installation since OVS is not required on the
    controller node.
  * Remove dhcp_agent.ini configuration (fix bug 1091846)

* Network node
  * Fix parameter name 'gateway_external_network_id'
    in /etc/quantum/l3_agent.ini
  * Add auth_url setting to /etc/quantum/l3_agent.ini (fix bug 1091892)
  * Add rabbit_host setting to quantum.conf on the network node.
  * Correct sql_connection in ovs_quantum_plugin.ini to point to MySQL
    on the controller node (fix bug 1091888)

* Compute node
  * Move nova-api-metadata service to the controller node since metadata
    service is usually running on the controller node
  * Move Open vSwitch configuration into a separate section

* Common
  * Remove unnecessary 'ip_forward = 1' from controller and compute nodes
  * Remove unnecessasry /etc/quantum/api-paste.ini configurations
    from the network and compute nodes (fix bug 1091878)

Fix bug 1091846
Fix bug 1091878
Fix bug 1091888
Fix bug 1091892

Change-Id: Ifc0e70183b1cd28400346eb7606e993de74dcbc3