Added small fix to post install section
Added small fix to post install section

1. Backup original bootstrap.
2. Fix reboot_bootstrap_nodes usage print.

Change-Id: I9cc0eaa4023a025472dab671fd7e8d200c906cfa

stackforge/fuel-plugin-mellanox,stackforge/fuel-plugin-mellanox,stackforge/fuel-plugin-mellanox,stackforge/fuel-plugin-mellanox