TES CLI: cancel fails on tasks with "SYSTEM ERROR" status

[pavelnikonorov]

The current implementation doesn't handle the cancel of task with "SYSTEM ERROR" status in cli/src/main.rs.

[uniqueg]

Would be good to add more details here (steps to reproduce, error logs etc). In particular, it is not clear whether this is a TES implementation issue or a GA4GH-SDK issue. If the latter, this may be a design issue, because (unless I'm missing something), the SDK should never set the status of a task itself, but rather take it from a call to GET /tasks/{id}.