Merge branch 'devel-2.5'

* devel-2.5:
  LUGroupAssignNodes: Fix node membership corruption
  LUGroupAssignNodes: Fix node membership corruption
  Fix pylint warning on unreachable code
  LUNodeEvacuate: Disallow migrating all instances at once
  Separate OpNodeEvacuate.mode from iallocator
  LUNodeEvacuate: Locking fixes
  Fix error when removing node

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