Use lvs instead of os.listdir in _cleanup_lvm

Compute user may not have permission to list /dev/<VolGroup>
directory. This results in error during instance cleanup and not
deleted lvm images, if libvirt driver use lvm images backend.
To prevent this, _cleanup_lvm use lvs command instead of os.listdir.

This fixes bug 1042710

Change-Id: I82ab4ca5ba3320f50c84e23839fcf6ed8f02be8c

etc/nova/rootwrap.d/compute.filters

@@ -185,5 +185,8 @@ lvremove: CommandFilter, /sbin/lvremove, root
 # nova/virt/libvirt/utils.py:
 lvcreate: CommandFilter, /sbin/lvcreate, root
 
+# nova/virt/libvirt/utils.py:
+lvs: CommandFilter, /sbin/lvs, root
+
 # nova/virt/libvirt/utils.py:
 vgs: CommandFilter, /sbin/vgs, root

nova/virt/libvirt/driver.py

@@ -565,7 +565,9 @@ class LibvirtDriver(driver.ComputeDriver):
             def fullpath(name):
                 return os.path.join(vg, name)
 
-            disk_names = filter(belongs_to_instance, os.listdir(vg))
+            logical_volumes = libvirt_utils.list_logical_volumes(vg)
+
+            disk_names = filter(belongs_to_instance, logical_volumes)
             disks = map(fullpath, disk_names)
             return disks
         return []

nova/virt/libvirt/utils.py

@@ -138,6 +138,17 @@ def volume_group_free_space(vg):
     return int(out.strip())
 
 
+def list_logical_volumes(vg):
+    """List logical volumes paths for given volume group.
+
+    :param vg: volume group name
+    """
+    out, err = execute('lvs', '--noheadings', '-o', 'lv_path', vg,
+                       run_as_root=True)
+
+    return [line.strip() for line in out.splitlines()]
+
+
 def remove_logical_volumes(*paths):
     """Remove one or more logical volume."""
     if paths: