Brick LVM: Handle space info as numeric types

Rather than relying on callers to cast values from the VG object
to float, always create them as floats up front.

This removes the nosuffix option used with the LVM commands in
Brick, as it does not appear to be used.

Also removes unneeded self.vg_pool_name variable.

Change-Id: Ic19ce206bc8069071e3c2d9e58ba5393119e9b4d
Merge "Brick LVM: Handle space info as numeric types"