Verify file consistency using centrally computed list

Until now “gnt-cluster verify” (LUClusterVerify) would compute its own
list of files to check for consistency. This list was not complete and
certain inconsistencies were missed.

With this patch the code is changed to use the list of files used by
LUClusterRedistConf. The new check needs to be on a whole-cluster level,
and no longer per node.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>