Avoid 'mda inconsistency' by properly registering UNLABELLED_PV flag (2.02.86).

Avoid 'mda inconsistency' by properly registering UNLABELLED_PV flag (2.02.86).

When a PV label write is deferred to a vg_write call (as introduced by a patch
in 2.02.86), the PV is flagged with the internal UNLABELLED_PV flag. However,
when calling vg_archive before vg_write, we still have the PV labelled with the
UNLABELLED_PV flag which was not recognised as a proper flag while exporting
VG metadata:

  # vgcreate vg /dev/sda
  No physical volume label read from /dev/sda
  Metadata inconsistency: Not all flags successfully exported.
  Metadata inconsistency: Not all flags successfully exported.
  Writing physical volume data to disk "/dev/sda"
  Physical volume "/dev/sda" successfully created
  Volume group "vg" successfully created