The api allows for creating, listing, and restoring of container
snapshots.  Snapshots are created as snapshot clones of the
original container - i.e. btrfs and lvm will be done as snapshot,
a directory-backed container will have overlayfs snapshots.  A
restore is a copy-clone, using the same backing store as the
original container had.

Changelog:

 . remove lxcapi_snap_open, which wasn't defined anyway.
 . rename get_comment to get_commentpath
 . if no newname is specified at restore, use c->name (as we meant to)
   rather than segving.
 . when choosing a snapshot index, use the correct path to check for.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>