LVM: remove redundant casts to float

The vg_free_space field is always assigned a float, so additional casts
are not necessary.

Change-Id: Ic2af78ba7dbd7388cc071fc2f0ea876a1558d0e9
Update SolidFire Driver to use cinder's units

The SolidFire driver uses math module and it's own
local GB variable.

This patch just removes that and uses the GiB def
that already exists in cinder.units.

Change-Id: I4fc167bd61dbb609bd325b4a32b120bf55db02fa
LVM: log thin pool name and size upon creation

The thin pool creation size may not be obvious to the user, so a log
message may help alleviate some confusion.

Change-Id: I3a98b610be612a4fb7496a89f9005012c9210bf8
Move clear_volume method to volume.utils

clear_volume was almost the same in LVM and BlockDevice drivers.
So it has been moved to utils.

Change-Id: Iadb6b8d01cf500109bb48b0d2c817109918519e0
Merge "LVM: log thin pool name and size upon creation"
Merge "Move clear_volume method to volume.utils"
Merge "LVM: remove redundant casts to float"