Make node deletion more stable

1. Use direct I/O for MBR erasing
2. Create pre-erase hook to avoid using
   of corrupted fs binaries
3. Use sysrq trigger to force node
   reset thus avoiding hanging reboot

Change-Id: Iafad920d9f2021bea374f58f828e5d33b820959d
Closes-bug: #1262524