Add support for erasing detected signatures on newly created LVs.
When creating a new LV, it's possible that the new LV will contain signatures from any previous use of this data area. If such signature is positioned within LV in a way that it makes it detectable for any tools scanning the LV (e.g. an automatic blkid scan run within udev for each new LV), we may end up with incorrect assumption that the signature found within LV data area is intended while in real it's not.
When creating a new LV and if there's any signature detected (in this LVM2 version it's MD, swap and LUKS signature), LVM tries to erase the signature first before properly activating the new LV. There's also an additional question for the user: "WARNING: <signature name> signature detected on <device name>. Wipe it? [y/n]" to confirm this signature wiping. Also, there's a new lvm.conf option "allocation/wipe_signatures_when_zeroing_new_lvs" (enabled by default) to enable or disable this feature.