fixed broken function where dict expected all lowercase key

root@gtest1:/var/gantryd# docker -v
Docker version 1.1.2, build d84a070

before this patch gantry would break like this:

root@gtest0:/var/gantryd# sudo ./gantryd.py update myapp -c myapp_web
Updating the image IDs on components
Traceback (most recent call last):
  File "./gantryd.py", line 83, in <module>
    start()
  File "./gantryd.py", line 80, in start
    action(dclient, args)
  File "./gantryd.py", line 43, in mark_updated
    dclient.markUpdated(args.component)
  File "/var/gantryd/gantryd/client.py", line 105, in markUpdated
    image_id = component.getImageId()
  File "/var/gantryd/runtime/component.py", line 69, in getImageId
    return result['id']
KeyError: 'id'