Improve npm run debug-test output

Previous output:

```
Running web tests with args: ~/projects/chromium/src/third_party/blink/tools/run_web_tests.py,inspector*,http/tests/inspector*,http/tests/devtools,--build-directory,~/projects/chromium/src/out,--target,Release,--additional-driver-flag=--debug-devtools,--additional-driver-flag=--remote-debugging-port=9222,--time-out-ms=6000000,runtime/runtime-evaluate-bad-unicode.js
```

This patch changes the output to:

```
Running web tests with args: ~/projects/chromium/src/third_party/blink/tools/run_web_tests.py inspector* http/tests/inspector* http/tests/devtools --build-directory ~/projects/chromium/src/out --target Release --additional-driver-flag=--debug-devtools --additional-driver-flag=--remote-debugging-port=9222 --time-out-ms=6000000 runtime/runtime-evaluate-bad-unicode.js
```

This way, the output contains the actual command that's being run, making it more readable and copy-paste friendly.

Change-Id: Ib5341514f3802937a052f1c5d257e45ee64c17a9
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2016751
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>
Auto-Submit: Mathias Bynens <mathias@chromium.org>
Reviewed-by: Tim van der Lippe <tvanderlippe@chromium.org>
diff --git a/scripts/npm_test.js b/scripts/npm_test.js
index e332287..c709cf6 100644
--- a/scripts/npm_test.js
+++ b/scripts/npm_test.js
@@ -272,7 +272,7 @@
     console.log('=============================================\n');
   }
   const args = [BLINK_TEST_PATH].concat(testArgs).concat(getTestFlags());
-  console.log(`Running web tests with args: ${args}`);
+  console.log(`Running web tests with args: ${args.join(' ')}`);
   childProcess.spawn(PYTHON, args, {stdio: 'inherit'});
 }