* 'occlum init' does not copy signing key file any more.
* 'occlum build' supports to set signing key and signing tool in args.
* 'occlum run' supports to run enclave in sgx release mode.
1. Now we support set App's env in Occlum.json, for example:
"env": [
"OCCLUM=yes",
"TEST=true"
]
2. Rewrite env test cases
3. Update Dockerfile to install "jq" tool