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


`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

/cc @keeb