zd3438 read node wrong

From zendesk ticket 3438.  The nuke exporter was not seeing the default transcode task.  Ends up this was because we were removing the last item in the export template rather than the initial one (which is the temporary Shotgun Shot creation task).  Fixing that makes it so that the nuke exporter sees the proper task and generates the nuke script appropriately.

While working through this issue, there was an issue with the default custom resolver, where it errored out if run against shots that had not yet been created.  Converted that to use the get_shot hook so that the shots are always there and linked up appropriately.