Ensure metadata is in sync with running node during tests (#333)

* add test-runtime crate to dynamically obtain metadata/node_runtime for tests

* cargo fmt

* Download substrate prior to cargo calls (hopefully)

* add README explaining test-runtime

* Fix CI, fmt and clippy

* more clippy

* tweak test-node readme

* fmt the clippied

* A little tidy up in build.rs

* use ureq and raw string

* Don't export unnecessary metadata

* async_std/RpcClient/bytes instead of ureq/Value/hex

* newline

* document try_from_url error unwrap

tests/integration/utils/node_proc.rs

@@ -64,13 +64,9 @@ where
 
     /// Attempt to kill the running substrate process.
     pub fn kill(&mut self) -> Result<(), String> {
-        log::info!("Killing contracts node process {}", self.proc.id());
+        log::info!("Killing node process {}", self.proc.id());
         if let Err(err) = self.proc.kill() {
-            let err = format!(
-                "Error killing contracts node process {}: {}",
-                self.proc.id(),
-                err
-            );
+            let err = format!("Error killing node process {}: {}", self.proc.id(), err);
             log::error!("{}", err);
             return Err(err)
         }