1094470 - Canceling a task that was already in a completed state now results in a 200 code instead of a 500
Updated the tasks docs to reflect the change of behaviour in task canceling
Added a better log message based on the PR review
Merge pull request #1094 from pulp/jcline-1094470

1094470 - Canceling a task that was already in a completed state now results in a 200 code instead of a 500