When vendored into moby, the local exporter uses a user map that results
in all files being given at most 755 permissions. This change updates
the test to use permissions less than or equal to that to make tests
equivalent whether running w/ dockerd worker or any other type.
Additionally, add assertions that exported images also have the expected
contents, which helps ensures consistency between images created by
dockerd and those created by vanilla buildkit.
Signed-off-by: Erik Sipsma <erik@sipsma.dev>
0539181757