task-combined: add a fix to allow running nested launchers
This allows running launcher web and get the launcher to run the web
entry of the procfile.
This enables us to set launcher as the command to run any other
command on buildpack-based images, allowing us to run ad-hoc commands
from the toolforge jobs run cli without having to manually specify
launcher <mycommand>.
Bug: T355214 Signed-off-by: David Caro dcaro@wikimedia.org