We introduce a WithSpecFromFile option combinator to allow creation
simpler creation of OCI specs from a file name. Often used as the first
option in a `SpecOpts` slice, it simplifies choosing between a local
file and the built-in default.
The code in `ctr run` has been updated to use the new option, with out
changing the order of operations or functionality present there.
Signed-off-by: Stephen Day <stephen.day@getcruise.com>
This changes the Windows runtime to use the snapshotter and differ
created layers, and updates the ctr commands to use the snapshotter and differ.
Signed-off-by: Darren Stahl <darst@microsoft.com>
