Wiping out md and lvm devices before partitioning

This change is intended to wipe out md and lvm
metadata which could remain on a disk. We do it
in 3 steps
1) we wipe out all md and lvm devices
2) we put 1M of zeros at the beginning of every new partition
3) we again wipe out all md and lvm devices

For details see comments in fuel_agent/fuel_agent/manager.py

Implements: blueprint image-based-provisioning
Change-Id: I55f18bd22f5609da18e33f1b238176c3bb95d327
Merge "Wiping out md and lvm devices before partitioning"