metadata: ask for confirmation before really initializing/removing PV that is marked...

metadata: ask for confirmation before really initializing/removing PV that is marked as belonging to a VG

Ask for confirmation when using pvcreate/pvremove on a PV which is
marked as belonging to a VG, just like we do in case of a PV which
belongs to known VG:

$ pvcreate -ff /dev/sda
Really INITIALIZE physical volume "/dev/sda" that is marked as belonging to a VG [y/n]? n
  /dev/sda: physical volume not initialized

$ pvremove -ff /dev/sda
Really WIPE LABELS from physical volume "/dev/sda" that is marked as belonging to a VG [y/n]? n
  /dev/sda: physical volume label not removed