Group the exceptions into the following groups
* Storage
* Jobs
* Execution
* Other (wrapped failure here)
This grouping makes it easier to understand where
one type of exception should be used vs using another
type of exception.
Backwards incompatible changes:
* StorageError -> StorageFailure
* AlreadyExists -> Duplicate
* WrappedFailure now inherits from Exception
and not directly from TaskFlowException since it
wraps arbitrary other exceptions and is not
specific to taskflow.
Cleanups:
* JobNotFound -> NotFound
* EmptyFlow -> Empty
* JobAlreadyExists -> AlreadyExists
* InvariantViolation (X)
* ConnectionFailure (X)
Change-Id: I0e1e81b513fbbc7adb8bfaa1244993e345ab70d3
a570aead53