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/lib.rs

@@ -0,0 +1,25 @@
+pub mod utils;
+pub mod wasi_wrappers;
+
+use libc;
+use std::ffi::CString;
+use std::io;
+use wasi::wasi_unstable;
+
+pub fn open_scratch_directory(path: &str) -> Result<wasi_unstable::Fd, String> {
+    // Open the scratch directory.
+    let dir_fd: wasi_unstable::Fd = unsafe {
+        let cstr = CString::new(path.as_bytes()).unwrap();
+        libc::open(cstr.as_ptr(), libc::O_RDONLY | libc::O_DIRECTORY)
+    } as wasi_unstable::Fd;
+
+    if (dir_fd as std::os::raw::c_int) < 0 {
+        Err(format!(
+            "error opening scratch directory '{}': {}",
+            path,
+            io::Error::last_os_error()
+        ))
+    } else {
+        Ok(dir_fd)
+    }
+}