Brick LVM: Handle space info as numeric types

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