add defaultFS and use OCIError
add defaultFS and use OCIError

Signed-off-by: liangchenye <49f3f795d1fda22b7f7dfee719201384e22b7d55@huawei.com>

opencontainers/ocitools,liangchenye/ocitools,wking/ocitools-v2,opencontainers/ocitools,liangchenye/ocitools,opencontainers/runtime-tools,opencontainers/runtime-tools,wking/ocitools-v2