smartos : add detection of GZ and make manifest persists across reboots

When started on a Global Zone (GZ) (or baremetal), SmartOS imports
manifests from /opt/custom/smf/ automatically.

This patch use dedicated SmartOS manifest from Salt.
Merge pull request #127 from virtua-network/add_virt_detection

SmartOS : Add detection of GZ and make manifest persists across reboots.