Enhancements to the Cisco Plugin to support multiple switches and smart vlan assignment

Scope: A few enhancements to the Cisco Nexus plugin to support multiple switches and some intelligence in the plugin when trunking vlans on those switches.

Use Cases: Quantum with the Cisco plugin (nexus subplugin)

Implementation Overview: The plugin communicates with Nova api when an instance is networked during creation, grabs the host that the instance is running on. Cross references that host with a topology config that tells the plugin what port/switch that host is connected to and trunks it on that switch/port.

Data Model Changes: Two fields added to model NexusPortBinding
                                     switch_ip = Column(String(255))
                                     instance_id = Column(String(255))

Configuration variables: nexus.ini config changed to-
[SWITCH]
# Ip address of the switch
[[172.18.112.37]]
# Hostname of the node
[[[asomya-controller.cisco.com]]]
# Port this node is connected to on the nexus switch
ports=1/1
# Hostname of the node
[[[asomya-compute.cisco.com]]]
# Port this node is connected to on the nexus switch
ports=1/2
# Port number where the SSH will be running at the Nexus Switch, e.g.: 22 (Default)
[[[ssh_port]]]
ssh_port=22

credentials.ini should include keystone credentials and endpoint-
# Provide credentials and endpoint
# for keystone here
[keystone]
auth_url=http://172.18.112.47:35357/v2.0
username=admin
password=abcd

API's: n/a

Plugin Interface: n/a

Required Plugin support: The cisco plugin configuration should include the aforementioned values.

Dependencies: nova-api, keystone

CLI Requirements: n/a

Horizon Requirements: n/a

Usage Example: n/a

Test Cases: n/a