report: Shift (u)sed pv_attr under (a)llocatable.

report: Shift (u)sed pv_attr under (a)llocatable.

Showing 'u' in the pv_attr reporting field is mostly unnecessary because
most PVs are allocatable, and being allocatable implies it is (u)sed,
and this is already obvious from other fields in the default 'pvs'
output like the VG name.

So move the new (u)sed pv_attr from character position 4 to 1, and only
show it in those rare cases when the PV is not (a)llocatable or the
relevant metadata is missing.

(Scripts should not be using pv_attr, but rather pv_allocatable,
pv_exported, pv_missing, pv_in_use etc.)