VMTools: services/apps use config env settings to override unhandled system env

VMTools: services/apps use config env settings to override unhandled system env
settings

Previously, only the VMToolsd service and user process would use the
config file set or unset environment settings, and only when the process name
was known (vmsvc, vmusr).

The code to process the config environment variables has moved from tools core to
vmtools library.