Allow PATH in rc service environment

Summary:
FreeBSD rc service allows to use <service name>_env variable to modify
environment, and already call env for that, so there is no need
to call a second time env.

This fixes an issue where $PATH wasn't defined, and so any command not
called with absolute path failed when called from a HTTP request.

Fixes T1968.

Test Plan: Tested on Hervil, git is now found

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1968

Differential Revision: https://devcentral.nasqueron.org/D3333