network improvement: add vms field

Add vms field for network GET method
update API.md

add a function to get all vms attach to a network
update model

add vms field for Network Resource property
update controller

Now get the info of default network:
$ curl -u <user>:<password> -H 'Content-type: application/json' -H 'Accept:
application/json' -X GET http://localhost:8000/networks/default
{
  "subnet":"192.168.122.0/24",
  "connection":"nat",
  "name":"default",
  "autostart":true,
  "state":"active",
  "interface":"virbr0",
  "dhcp":{
    "start":"192.168.122.2",
    "end":"192.168.122.254"
  },
  "vms":[
    "rhel6",
    "opensuse12"
  ]
}
we can see, there are two vms attched to this network

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
network improvement: update mockmodel to support vms field

get all vms attach to a network

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>
network improvement: update test case to support vms field

update test_rest and test_model

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>