Do not stringify errors when logging them

Converting errors to string drops their stack trace, making it more
difficult to debug their actual reason. We can instead pass the error
objects as-is to console.warn/error, so that Firefox/Chrome devtools
will show both the stack trace of the console.warn/error call, and the
original stack trace of the error.

This commit also enables the `unicorn/no-console-spaces` ESLint rule,
which avoids accidental extra spaces when passing multiple parameters to
`console.*` methods.

test/downloadutils.mjs

@@ -86,7 +86,7 @@ async function downloadManifestFiles(manifest) {
     try {
       await downloadFile(file, url);
     } catch (ex) {
-      console.error(`Error during downloading of ${url}: ${ex}`);
+      console.error(`Error during downloading of ${url}:`, ex);
       fs.writeFileSync(file, ""); // making it empty file
       fs.writeFileSync(`${file}.error`, ex);
     }

test/driver.js

@@ -1192,7 +1192,7 @@ class Driver {
         resolve();
       })
       .catch(reason => {
-        console.warn(`Driver._send failed (${url}): ${reason}`);
+        console.warn(`Driver._send failed (${url}):`, reason);
 
         this.inFlightRequests--;
         resolve();

test/unit/testreporter.js

@@ -18,7 +18,7 @@ const TestReporter = function (browser) {
           resolve();
         })
         .catch(reason => {
-          console.warn(`TestReporter - send failed (${action}): ${reason}`);
+          console.warn(`TestReporter - send failed (${action}):`, reason);
           resolve();
 
           send(action, json);