Merge branch 'stable-2.7' into stable-2.8

Merge branch 'stable-2.7' into stable-2.8

* stable-2.7:
  Bump up version for 2.7.0~rc2 release
  Add NEWS entry for SO_PEERCRED fix
  Workaround missing SO_PEERCRED
  Add debugging clause to _ExpandCheckDisks error
  Mention hail network incompatibility in manpages
  Remove obsolete Debian-related documentation
  Update NEWS for 2.7.0 rc2
  Improve installation documentation
  Fix owner of the OS log dir

Conflicts:
	lib/cmdlib.py: port to cmdlib/instance_storage.py
	lib/tools/ensure_dirs.py: trivial

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>