Brick LVM: Set C locale when gathering PV info

Some locales use commas as decimal separators, which means
that code breaks when someone expects to be able to use the
PV size as a float.

Change-Id: Idceb405e021ea8a0f44e19be43bad1307fbbb51c
Related-Bug: 1219963
Merge "Brick LVM: Set C locale when gathering PV info"