Description of problem:
`virsh vol-list --pool VG` does not list existing thin volumes.

Basically, anything what's in /dev/VG directory should be visible (the only exceptions are thin-pool and cache-pool volumes).

It is possible to use "role" fields (see `lvs -o+role` output) to filter out any "private" devices (column matching perl-re `/(,|^)private(,|$)/` or using lvm's select: `lvs -S role=public`).

I checked at least mirror and RAID1 volumes work fine.
Looks it is only thin-volumes not present.

Version-Release number of selected component (if applicable):

libvirt-*-1.2.17-13.el7_2.5.x86_64

It is the same on F25:

libvirt-*-2.0.0-2.fc25.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Prepare the env:

    Create a Logical storage pool # You know better how to automate this...
    Let vg0 be both the name of the volume group and of the pool.

2. As root create a thin-pool and thin-volumes:

    #!/bin/bash

    # TODO: modify these as appropriate
    VG=vg0 # name of the VG from step 0.1
    POOL=pool1
    THINLV=thin
    LV=linear
    # choose whatever small size here, we will not continue with installation:
    SIZEOFPOOL=16M
    SIZEOFTHINVOL=16M
    SIZEOFVOL=16M

    # Create pool and thin-volumes (and regular one to check feature works at all)
    lvcreate --type thin --thin-pool $VG/$POOL -L $SIZEOFPOOL -n $THINLV -V $SIZEOFTHINVOL
    lvcreate -n $LV -L $SIZEOFVOL $VG

    # Refresh pool:
    virsh pool-refresh $VG

    # list volumes:
    virsh vol-list --pool $VG


Assuming THINLV is "thin" and LV is "linear":

Actual results:
Only the "linear" volume is present

Expected results:
Both "thin" and "linear" volumes should be there.