detect: pdisk shall be reported in GB

Up to now, the pdisk size were not reported in consistent units. For
example, we had :
    ('pdisk', 'disk3', 'size', '3.637'),

This is perfectly incorrect since its a 3 TB disk drive.

To avoid this, the size shall be passed through the size_in_gb()
function to insure the unit to be GB.
detect: Fixing size_in_gb() behavior with float TB

pdisk sizes does report float numbers of storage like :  3.637 TB

Adding three zero (0) at the end of this number would turn it in
3.637000 GB which is wrong.

This patch does consider this field as float numbers, multiple it by
1000 and convert it back to a string representation of the integer
value.

As a result, the 3.637 TB becomes 3637 GB an not 3.637