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/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+name = "wasi-tests"
+version = "0.0.0"
+authors = ["The Wasmtime Project Developers"]
+readme = "README.md"
+edition = "2018"
+publish = false
+
+[dependencies]
+libc = "0.2.65"
+wasi = "0.7.0"
+more-asserts = "0.2.1"
+
+# This crate is built with the wasm32-wasi target, so it's separate
+# from the main Wasmtime build, so use this directive to exclude it
+# from the parent directory's workspace.
+[workspace]