run devstack with cisco plugin

Add support in devstack to run it with cisco plugin.

A couple of variables can be defined in localrc to customize the cisco plugin:

-- Q_CISCO_PLUGIN_SUBPLUGINS: defines the subplugins that will be deployed. This is a bash indexed array. the possible values for the array elements are "nexus", "openvswitch", "n1kv". Note that "openvswitch" and "n1kv" shouldn't be used together. An example is:

               declare -a Q_CISCO_PLUGIN_SUBPLUGINS=(nexus openvswitch)

If Q_CISCO_PLUGIN_SUBPLUGINS is not defined in localrc, it is defined as (nexus openvswitch) by default.

-- Q_CISCO_PLUGIN_SWITCH_INFO: defines the nexus switch information used in the deployment. This is a bash associative array with nexus switch ip addresses as keys. The value has the format as <username>:<password>:<ssh_port>[:<compute-host-name>:<nexus-port-connected-with>]. Essentially, it defines the switch's access information, and the compute hosts that are connected to the switch. An example looks like

             declare -A Q_CISCO_PLUGIN_SWITCH_INFO=
                           ([1.1.1.1]=admin:mySecretPassword:22:compute1:1/1:compute2:1/2
                            [2.2.2.2]=root:root:22:compute3:1/1:compute4:1/2)

If Q_CISCO_PLUGIN_SWITCH_INFO is not defined in localrc, it assumes no switch is used in the deployment. If the nexus subplugin is deployed (as indicated by the Q_CISCO_PLUGIN_SUBPLUGINS array), a fake switch (with a fake driver) will be deployed.