controller: Don't include deleted formations in formation stream

[lmars]

Schedulers in a cluster restored from a backup were failing to stream formation updates with the following error:

t=2016-05-16T15:51:50+0000 lvl=info msg="connecting formation event stream" component=scheduler fn=streamFormationEvents
t=2016-05-16T15:51:50+0000 lvl=warn msg="formation event stream disconnected" component=scheduler fn=streamFormationEvents err="Server error: controller: resource not found"

The stream was being closed because the controller was trying to expand deleted formations, hitting ErrNotFound when looking up the associated release and returning that to the stream.

I have updated the formation_list_since query (along with some others) to check for deleted_at IS NULL.

[josephglanville]

Good catch, LGTM.