lxd/storage/drivers/utils: Adds blockDevSizeBytes function
lxd/storage/drivers/utils: Adds blockDevSizeBytes function

For retrieving size of block devices in bytes.

Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,stgraber/lxd,Skarlso/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,Skarlso/lxd,lxc/lxd,hallyn/lxd,stgraber/lxd,hallyn/lxd,Skarlso/lxd,mjeanson/lxd,mjeanson/lxd,Skarlso/lxd,mjeanson/lxd,atxwebs/lxd,stgraber/lxd,lxc/lxd,atxwebs/lxd,lxc/lxd,lxc/lxd,lxc/lxd,stgraber/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd