Fix: worker structure is leaked in run_as process

Fix: worker structure is leaked in run_as process

The run_as structure (handle) is allocated and initialized before
the fork() that spawns the run_as process. Currently, that structure
is only cleaned-up on the parent's end.

This fix performs the clean-up on the worker's side as well.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>