Description of problem:
I have two tasks I can not cancel and they are blocking content host deletions


Version-Release number of selected component (if applicable):
satellite-6.2.0-9.0.beta.el7sat.noarch


How reproducible:
rarely


Steps to Reproduce:
1. Register 50 RHEL7 systems concurrently with subscription-manager through
   capsule, some of the registrations fails
2. Attempt to delete these content hosts


Actual results:
2 of the sub-tasks fails, because they are blocked by:

https://<fqdn>/foreman_tasks/tasks/5bc45616-a3ed-4a2a-a3ab-db95f07cd1f2
  Id: 5bc45616-a3ed-4a2a-a3ab-db95f07cd1f2
  Label: Actions::Katello::Host::Register
  Name: Register Host d21d8ba86acb
  Owner: admin
  Execution type: Delayed
  Start at: 2016-04-29 07:18:28 +0200
  Start before: -
  Started at: 2016-04-29 07:18:28 +0200
  Ended at:
  State: running
  Result: - 
  ...progress bar shows 67%
  ...both "Resume" and "Cancel" buttons are inactive
  ...DynFlow console do not have skip link, I do not see a way how to cancel

https://<fqdn>/foreman_tasks/tasks/6dd28861-ba39-4da6-9fc9-caad105a4e01
  Id: 6dd28861-ba39-4da6-9fc9-caad105a4e01
  Label: Actions::Katello::Host::Register
  Name: Register Host 7fe0a391bcd8
  Owner: admin
  Execution type: Delayed
  Start at: 2016-04-29 07:23:02 +0200
  Start before: -
  Started at: 2016-04-29 07:23:02 +0200
  Ended at:
  State: running
  Result: - 
  ...progress bar shows 100%
  ...both "Resume" and "Cancel" buttons are inactive
  ...DynFlow console do not have skip link, I do not see a way how to cancel


Expected results:
It should not happen, but when it happens, it should be possible to safely cancel any tasks