pvesm status: improve output and its format

pvesm status: improve output and its format

Add column names at top of output, this allows easier understanding
of what each column means.

Use leading spaces on the percentage column so that this is lined up.

Switch out the 1/0 from the active column with the actual status
(active, inactive, disabled).

Show N/A if storage is disabled.

Use $res->{total} instead of calculating a sum of used and available.

Remove wrong rounding - if we want to display 2 digits from the
fractional part we would need to add 0.005 not 0.5, this made the
result quite wrong depending on the storage size.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>