grim/convey

update convey/clean to use the Runtime.ConfigPath instead of the working directory.

Fixes CONVEY-189
# This is a simple test that makes sure the clean task can remove files that
# have an environment variable in their name.
---
environment:
- HOST_PATH=.
tasks:
clean:
type: convey/clean
files:
- ${HOST_PATH}/dirty
- ${HOST_PATH}/**/bar.baz
plans:
default:
stages:
- tasks: clean