Fix format_device() for new vold paths

This completes the previous patch committed: https://github.com/CyanogenMod/android_bootable_recovery/commit/f4c69bf953881288088be92751712fe92ed94dbd
This how we should always check for valid volumes in recovery start of vold changes to data/media devices

Change-Id: I6912b1b2a473ea8737ea3e415e9a0172bb35eff1