To work better with Kata containers, we need to delete() from the
OCI runtime as a part of cleanup, to ensure resources aren't
retained longer than they need to be.
To enable this, we need to add a new state to containers,
ContainerStateExited. Containers transition from
ContainerStateStopped to ContainerStateExited via cleanupRuntime
which is invoked as part of cleanup(). A container in the Exited
state is identical to Stopped, except it has been removed from
the OCI runtime and thus will be handled differently when
initializing the container.
Signed-off-by: Matthew Heon <matthew.heon@gmail.com>