1. All generated, build files are now in a separate build directory;
2. The CLI tool supports three sub-commands: init, build, and run;
3. Refactor tests to use the new tool.
* Add patch to Rust SGX SDK to enable integrity-only SgxFile
* Upgrade to the new SEFS extended with the integrity-only mode
* Use integrity-only SEFS for /bin and /lib in test
* Add the MAC of integrity-only SEFS to Occlum.json in test
* Mount multiple FS according to Occlum.json
* Check the MACs of integrity-only SEFS images