Brick LVM: Rename get_all_volumes, further optimize

This method can process all LVs, those in a VG, or an
individual LV.  Rename it to be more descriptive.

Optimize update_volume_group_info check for thin pool.

Remove volume.utils.get_all_volumes, which is unused.

Remove fake_lvm.get_all_volumes and
fake_lvm.get_all_volume_groups which don't appear to
have correct signatures/returns and are unused.

Change-Id: I412c62230517cbfc08cc0076aaeea45224e6b50e
Merge "Brick LVM: Rename get_all_volumes, further optimize"