lxd/storage/drivers/generic/vfs: Adds support for custom volume backups to genericVFSBackupVolume
lxd/storage/drivers/generic/vfs: Adds support for custom volume backups to genericVFSBackupVolume

Co-authored-by: Thomas Hipp <5f82c492b3b00e427412d216ce820707a10c51ce@canonical.com>
Signed-off-by: Thomas Parrott <6b778ce645fb0e3dde76d79eccad490955b1ae74@canonical.com>

hallyn/lxd,atxwebs/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,hallyn/lxd,stgraber/lxd,lxc/lxd,lxc/lxd,hallyn/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,atxwebs/lxd,stgraber/lxd,atxwebs/lxd,lxc/lxd,stgraber/lxd,lxc/lxd,lxc/lxd