[plan-build] Support setting `$pkg_service_run` with svc path vars.
[plan-build] Support setting `$pkg_service_run` with svc path vars.

habitat-sh/habitat,nathenharvey/habitat,georgemarshall/habitat,nathenharvey/habitat,rsertelon/habitat,habitat-sh/habitat,georgemarshall/habitat,nathenharvey/habitat,georgemarshall/habitat,habitat-sh/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,rsertelon/habitat,habitat-sh/habitat,habitat-sh/habitat,georgemarshall/habitat,georgemarshall/habitat,nathenharvey/habitat,habitat-sh/habitat,georgemarshall/habitat,rsertelon/habitat,nathenharvey/habitat,nathenharvey/habitat,habitat-sh/habitat,georgemarshall/habitat,georgemarshall/habitat,habitat-sh/habitat,rsertelon/habitat