When cancel taskRun, the pipelineRun state should be Cancelled, not Failed.

[assertion]

Expected Behavior

When I change the state of a taskRun to TaskRunCancelled, the state of pipelineRun should be PipelineRunCancelled. And the state of taskRun and pipelineRun will be consistent.

Actual Behavior

Now if I change the taskRun to Cancelled, the pipelineRun state will be changed to Failure.
In pkg/reconciler/pipelinerun/resources/pipelinerunresolution.go, there's IsDone, isFailure, isSuccessfully, isSkipped functions to check and calculate the state of pipelineRun, but there's no something like isCancelled function.

Steps to Reproduce the Problem

1. Create a pipelineRune with some taskRuns.
2. Cancel one running taskRun by updating its spec to mark it as cancelled. Cancelling a TaskRun
   
3. Watch the state of pipelineRun.

Additional Info

[vdemeester]

/kind feature
/area api