Merge branch 'stable-2.8'

Merge branch 'stable-2.8'

* stable-2.8:
  Bump up version for 2.7.0~rc2 release
  Create overall design document for 2.8
  Add NEWS entry for SO_PEERCRED fix
  Workaround missing SO_PEERCRED
  Add debugging clause to _ExpandCheckDisks error
  Reduce pylint maximum file length to 4500
  Mention hail network incompatibility in manpages
  Remove obsolete Debian-related documentation
  Update NEWS for 2.7.0 rc2
  Improve installation documentation
  Add Harep man page
  Stash Xen config file after a failed startup
  Fix owner of the OS log dir

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>