Merge branch 'stable-2.5' into devel-2.5

* stable-2.5:
  LUGroupAssignNodes: Fix node membership corruption
  Fix pylint warning on unreachable code
  LUNodeEvacuate: Disallow migrating all instances at once
  LUNodeEvacuate: Locking fixes
  Fix error when removing node

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>