Hangs when using example tasks/plugins

[IRCody]

When running the example task under examples/tasks/mock-file.json It has an error:

ERRO[0080] error with processor job                      _module=scheduler-job block=run content-type=snap.gob error=plugin pool not found job-type=processor plugin-config=map[] plugin-name=passthru plugin-version=-1

This causes snapd to hang. It doesn't respond to ctrl+c. The task is shown as still running in using snapctl task list but has only a single hit. It seems like it might be related to the changes from #743 since I do not get the error if I reset before that.

Steps to reproduce:

snapd -t 0 -l 1

Then load the plugins:

snapctl plugin load ../plugin/snap-collector-mock1
snapctl plugin load ../plugin/snap-collector-mock2
snapctl plugin load ../plugin/snap-publisher-file
snapctl plugin load ../plugin/snap-processor-passthru

Create the task:

snapctl task create -t examples/tasks/mock-file.json

[geauxvirtual]

This bug was introduced with PR #743.