Merge branch 'stable-2.6' into devel-2.6

* stable-2.6:
  Make stable-2.6 compatible with newer pep8
  Fix computation of disk sizes in _ComputeDiskSize
  Add verification of RPC results in _WipeDisks
  Add test for checking that all gnt-* subcommands run OK
  Fix double use of PRIORITY_OPT in gnt-node migrate
  Add new Makefile target to rebuild the whole dist

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>