Add image name in /events

`docker run base ls` will produce:

    [2013-08-12 11:56:58 +0000 UTC] 0481fb861278: (from base:latest) create
    [2013-08-12 11:56:58 +0000 UTC] 0481fb861278: (from base:latest) start
    [2013-08-12 11:56:58 +0000 UTC] 0481fb861278: (from base:latest) die

    {"status":"create","id":"0481fb861278","from":"base:latest","time":1376308618}
    {"status":"start","id":"0481fb861278","from":"base:latest","time":1376308618}
    {"status":"die","id":"0481fb861278","from":"base:latest","time":1376308618}

`docker run centos env` will produce:

    [2013-08-12 11:58:14 +0000 UTC] eeaabc9d2995: (from centos:6.4) create
    [2013-08-12 11:58:14 +0000 UTC] eeaabc9d2995: (from centos:6.4) start
    [2013-08-12 11:58:14 +0000 UTC] eeaabc9d2995: (from centos:6.4) die


    {"status":"create","id":"eeaabc9d2995","from":"centos:6.4","time":1376308694}
    {"status":"start","id":"eeaabc9d2995","from":"centos:6.4","time":1376308694}
    {"status":"die","id":"eeaabc9d2995","from":"centos:6.4","time":1376308694}

/cc @keeb