lxd/storage/utils: Renames and reworks VolumeSnapshotsGet to VolumeDBSnapshotsGet
lxd/storage/utils: Renames and reworks VolumeSnapshotsGet to VolumeDBSnapshotsGet

Updated to accept a pool ID rather than running an additional query to convert pool name to ID.

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

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