Start to update the wasi crate in wasi tests (#675)

* Move `wasi` to `wasi_old` in wasi-tests

Leave space for the new `wasi` crate but allow us to incrementally
update tests.

* Update the big_random_buf test

* Update clock_time_get test

* Update close_preopen test

* Review comments

* Update to latest Wasmtime API

crates/test-programs/build.rs

@@ -30,6 +30,8 @@ mod wasi_tests {
                 println!("cargo:rerun-if-changed={}", test_file_path);
             }
         }
+        println!("cargo:rerun-if-changed=wasi-tests/Cargo.toml");
+        println!("cargo:rerun-if-changed=wasi-tests/src/lib.rs");
         // Build tests to OUT_DIR (target/*/build/wasi-common-*/out/wasm32-wasi/release/*.wasm)
         let out_dir = PathBuf::from(
             env::var("OUT_DIR").expect("The OUT_DIR environment variable must be set"),