Merge branch 'stable-2.6' into devel-2.6

Merge branch 'stable-2.6' into devel-2.6

* stable-2.6:
  Fix typo in gnt-instance man page
  jqueue: Return jobs to queue when shutting down
  gnt-debug delay: Add "--submit" option
  Make hostname checks uniform between instance rename and add
  Improve logging of new job submissions
  Improve handling of lock exceptions
  Add note about developing on a production machine
  Fix runtime memory increases
  Fix validation of vgname in OpClusterSetParams
  Fix removal of storage directory on shared file storage
  Switch non-redundant check to disk template-based
  Document the new --yes-do-it option for master-failover
  Add option to force master-failover without voting
  Update instance modify message
  Force tap's MAC prefix to "fe"
  Fix disk adoption interaction with ipolicy checks
  Better NEWS file for 2.6.1

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>