Clean up any/all stale partition tables.

When formatting media as a public volume, we write an MBR, but we
might leave a stale GPT floating around.  Some devices are configured
to aggressively prefer GPT when detected, even if the checksums
between primary/secondary don't match.

To work around this, nuke both MBR and GPT tables from the media
before we lay down our new MBR.

Bug: 24112219
Change-Id: Ibf1be466a6877cbab925a24db5e5dbab0613bea7
1 file changed