Reorganize wasi-misc-tests. (#575)

* Reorganize wasi-misc-tests.

Move wasi-misc-tests out of wasi-common, to break a dependency cycle;
previously, wasmtime-* depended on wasi-common, but wasi-common
dev-dependended on wasmtime-*.

Now, wasi-common no longer dev-depends on wasmtime-*; instead, the
tests are in their own crate which depends on wasi-common and on
wasmtime-*.

Also, rename wasi-misc-tests to wasi-tests for simplicity.

This also removes the "wasm_tests" feature; it's replaced by the
"test-programs" feature.

* Update the CI script to use the new feature name.

* Update the CI script to use the new feature name in one more place.

* Change a `write!` to a `writeln!`.

crates/test-programs/wasi-tests/src/utils.rs

@@ -0,0 +1,54 @@
+use crate::wasi_wrappers::*;
+use more_asserts::assert_gt;
+use wasi::wasi_unstable;
+
+pub unsafe fn create_dir(dir_fd: wasi_unstable::Fd, dir_name: &str) {
+    assert!(
+        wasi_path_create_directory(dir_fd, dir_name).is_ok(),
+        "creating a directory"
+    );
+}
+
+pub unsafe fn cleanup_dir(dir_fd: wasi_unstable::Fd, dir_name: &str) {
+    assert!(
+        wasi_path_remove_directory(dir_fd, dir_name).is_ok(),
+        "remove_directory on an empty directory should succeed"
+    );
+}
+
+/// Create an empty file with the given name.
+pub unsafe fn create_file(dir_fd: wasi_unstable::Fd, file_name: &str) {
+    let mut file_fd = wasi_unstable::Fd::max_value() - 1;
+    let status = wasi_path_open(
+        dir_fd,
+        0,
+        file_name,
+        wasi_unstable::O_CREAT,
+        0,
+        0,
+        0,
+        &mut file_fd,
+    );
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "creating a file"
+    );
+    assert_gt!(
+        file_fd,
+        libc::STDERR_FILENO as wasi_unstable::Fd,
+        "file descriptor range check",
+    );
+    close_fd(file_fd);
+}
+
+pub unsafe fn cleanup_file(dir_fd: wasi_unstable::Fd, file_name: &str) {
+    assert!(
+        wasi_path_unlink_file(dir_fd, file_name).is_ok(),
+        "unlink_file on a symlink should succeed"
+    );
+}
+
+pub unsafe fn close_fd(fd: wasi_unstable::Fd) {
+    assert!(wasi_unstable::fd_close(fd).is_ok(), "closing a file");
+}