Add more fields to TaskResponse

- State
- Failed
- FailureReason
- Result

[#79618146, #79618144, #79618148]

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotal.io>
Backfill tests for Task serialization/deserialization

Signed-off-by: Max Brunsfeld <mbrunsfeld@pivotal.io>